diff --git a/e2e/README.md b/e2e/README.md
index c39d3af31..88820c3c3 100644
--- a/e2e/README.md
+++ b/e2e/README.md
@@ -39,8 +39,9 @@ comes from the deployment URL returned by `vc deploy --prebuilt`.
 One-time project setup:
 
 - Configure the shared Vercel project for Node.js 24.
-- Provide the model-provider credentials the fixtures need (the agents and
-  judges run against `openai/gpt-5.5`) in the project's Preview environment.
+- Provide the model-provider credentials the fixtures need (the gateway-backed
+  agents and judges run against `openai/gpt-5.6-sol`) in the project's Preview
+  environment.
 - Provide `VERCEL_TOKEN`, `VERCEL_ORG_ID`, and `VERCEL_PROJECT_ID` in CI.
 
 Run a fixture against Vercel from its directory:
@@ -80,17 +81,16 @@ must run against the alias — the `e2e-vercel` workflow sets
 evals as a second `eve eval` invocation after the main suite. Without the
 alias env (local matrix, plain `eve eval --strict`) the eval skips.
 
-Most fixture agents run against `anthropic/claude-sonnet-5` and judges run
-against `openai/gpt-5.5`. Both are real models, so the environment must provide
-the corresponding model-provider credentials. `agent-prompt-cache` is the one
-fixture that authors a direct `@ai-sdk/anthropic` model instance instead of a
-gateway model id: its eval asserts the harness's Anthropic cache-breakpoint
-placement, which only runs on that path. The instance points at the AI
-Gateway's Anthropic-compatible Messages endpoint so it uses the same
-`AI_GATEWAY_API_KEY` credential as every other fixture. `agent-workflow-stress` uses eve's
-`mockModel` fixture helper so its 100-turn runs stay fast and deterministic. Its
-concurrent and sequential evals cover high-volume session execution and repeated
-session resumption respectively.
+Gateway-backed fixture agents and judges run against `openai/gpt-5.6-sol`.
+`agent-prompt-cache` is the one fixture that authors a direct
+`@ai-sdk/anthropic` model instance instead of a gateway model id: its eval
+asserts the harness's Anthropic cache-breakpoint placement, which only runs on
+that path. The instance points at the AI Gateway's Anthropic-compatible
+Messages endpoint so it uses the same `AI_GATEWAY_API_KEY` credential as every
+other fixture. `agent-workflow-stress` uses eve's `mockModel` fixture helper so
+its 100-turn runs stay fast and deterministic. Its concurrent and sequential
+evals cover high-volume session execution and repeated session resumption
+respectively.
 
 ## Fixtures
 
diff --git a/e2e/fixtures/agent-basic-runtime/agent/agent.ts b/e2e/fixtures/agent-basic-runtime/agent/agent.ts
index bea278ea3..7c4adca2c 100644
--- a/e2e/fixtures/agent-basic-runtime/agent/agent.ts
+++ b/e2e/fixtures/agent-basic-runtime/agent/agent.ts
@@ -1,6 +1,6 @@
 import { defineAgent } from "eve";
 
 export default defineAgent({
-  model: "openai/gpt-5.5",
+  model: "openai/gpt-5.6-sol",
   reasoning: "high",
 });
diff --git a/e2e/fixtures/agent-basic-runtime/evals/evals.config.ts b/e2e/fixtures/agent-basic-runtime/evals/evals.config.ts
index 6864dd176..912e6ec89 100644
--- a/e2e/fixtures/agent-basic-runtime/evals/evals.config.ts
+++ b/e2e/fixtures/agent-basic-runtime/evals/evals.config.ts
@@ -2,5 +2,5 @@ import { defineEvalConfig } from "eve/evals";
 
 /** Default judge model for any `t.judge.*` assertion in this fixture. */
 export default defineEvalConfig({
-  judge: { model: "openai/gpt-5.5" },
+  judge: { model: "openai/gpt-5.6-sol" },
 });
diff --git a/e2e/fixtures/agent-channels/agent/agent.ts b/e2e/fixtures/agent-channels/agent/agent.ts
index dc6d957f5..7c4adca2c 100644
--- a/e2e/fixtures/agent-channels/agent/agent.ts
+++ b/e2e/fixtures/agent-channels/agent/agent.ts
@@ -1,6 +1,6 @@
 import { defineAgent } from "eve";
 
 export default defineAgent({
-  model: "anthropic/claude-sonnet-5",
+  model: "openai/gpt-5.6-sol",
   reasoning: "high",
 });
diff --git a/e2e/fixtures/agent-channels/evals/evals.config.ts b/e2e/fixtures/agent-channels/evals/evals.config.ts
index 6864dd176..912e6ec89 100644
--- a/e2e/fixtures/agent-channels/evals/evals.config.ts
+++ b/e2e/fixtures/agent-channels/evals/evals.config.ts
@@ -2,5 +2,5 @@ import { defineEvalConfig } from "eve/evals";
 
 /** Default judge model for any `t.judge.*` assertion in this fixture. */
 export default defineEvalConfig({
-  judge: { model: "openai/gpt-5.5" },
+  judge: { model: "openai/gpt-5.6-sol" },
 });
diff --git a/e2e/fixtures/agent-model/agent/agent.ts b/e2e/fixtures/agent-model/agent/agent.ts
index 7400bd22a..fa66a26bc 100644
--- a/e2e/fixtures/agent-model/agent/agent.ts
+++ b/e2e/fixtures/agent-model/agent/agent.ts
@@ -7,7 +7,7 @@ import { defineAgent, defineDynamic, type DynamicResolveContext } from "eve";
  */
 export default defineAgent({
   model: defineDynamic({
-    fallback: "openai/gpt-5.5",
+    fallback: "openai/gpt-5.6-sol",
     events: {
       "turn.started": (_event, ctx) => {
         const text = lastUserText(ctx.messages);
@@ -18,7 +18,7 @@ export default defineAgent({
 
         if (text.includes("[model: mini]")) {
           return {
-            model: "openai/gpt-5.5-mini",
+            model: "openai/gpt-5.6-sol",
             modelContextWindowTokens: 128_000,
           };
         }
diff --git a/e2e/fixtures/agent-model/evals/dynamic-model/fallback.eval.ts b/e2e/fixtures/agent-model/evals/dynamic-model/fallback.eval.ts
index 09a44c505..2644c8596 100644
--- a/e2e/fixtures/agent-model/evals/dynamic-model/fallback.eval.ts
+++ b/e2e/fixtures/agent-model/evals/dynamic-model/fallback.eval.ts
@@ -16,7 +16,7 @@ export default defineEval({
       events.some(
         (event) =>
           event.type === "session.started" &&
-          event.data.runtime?.modelId === "dynamic:openai/gpt-5.5",
+          event.data.runtime?.modelId === "dynamic:openai/gpt-5.6-sol",
       ),
     );
   },
diff --git a/e2e/fixtures/agent-model/evals/dynamic-model/turn-selection.eval.ts b/e2e/fixtures/agent-model/evals/dynamic-model/turn-selection.eval.ts
index acd09bada..52b43b9b1 100644
--- a/e2e/fixtures/agent-model/evals/dynamic-model/turn-selection.eval.ts
+++ b/e2e/fixtures/agent-model/evals/dynamic-model/turn-selection.eval.ts
@@ -1,8 +1,8 @@
 import { defineEval } from "eve/evals";
 
 /**
- * A marked turn selects `openai/gpt-5.5-mini`; the next unmarked turn falls
- * back. Both completing proves each reference serves a real model call.
+ * A marked turn resolves an explicit per-turn model configuration; the next
+ * unmarked turn falls back. Both paths use `openai/gpt-5.6-sol`.
  */
 export default defineEval({
   description: "Dynamic model smoke: per-turn selection and null fallback in one session.",
diff --git a/e2e/fixtures/agent-model/evals/evals.config.ts b/e2e/fixtures/agent-model/evals/evals.config.ts
index 6864dd176..912e6ec89 100644
--- a/e2e/fixtures/agent-model/evals/evals.config.ts
+++ b/e2e/fixtures/agent-model/evals/evals.config.ts
@@ -2,5 +2,5 @@ import { defineEvalConfig } from "eve/evals";
 
 /** Default judge model for any `t.judge.*` assertion in this fixture. */
 export default defineEvalConfig({
-  judge: { model: "openai/gpt-5.5" },
+  judge: { model: "openai/gpt-5.6-sol" },
 });
diff --git a/e2e/fixtures/agent-openapi-swagger/agent/agent.ts b/e2e/fixtures/agent-openapi-swagger/agent/agent.ts
index dc6d957f5..7c4adca2c 100644
--- a/e2e/fixtures/agent-openapi-swagger/agent/agent.ts
+++ b/e2e/fixtures/agent-openapi-swagger/agent/agent.ts
@@ -1,6 +1,6 @@
 import { defineAgent } from "eve";
 
 export default defineAgent({
-  model: "anthropic/claude-sonnet-5",
+  model: "openai/gpt-5.6-sol",
   reasoning: "high",
 });
diff --git a/e2e/fixtures/agent-openapi-swagger/evals/evals.config.ts b/e2e/fixtures/agent-openapi-swagger/evals/evals.config.ts
index 6864dd176..912e6ec89 100644
--- a/e2e/fixtures/agent-openapi-swagger/evals/evals.config.ts
+++ b/e2e/fixtures/agent-openapi-swagger/evals/evals.config.ts
@@ -2,5 +2,5 @@ import { defineEvalConfig } from "eve/evals";
 
 /** Default judge model for any `t.judge.*` assertion in this fixture. */
 export default defineEvalConfig({
-  judge: { model: "openai/gpt-5.5" },
+  judge: { model: "openai/gpt-5.6-sol" },
 });
diff --git a/e2e/fixtures/agent-prompt-cache/evals/evals.config.ts b/e2e/fixtures/agent-prompt-cache/evals/evals.config.ts
index e9b6c4d05..e05d9f344 100644
--- a/e2e/fixtures/agent-prompt-cache/evals/evals.config.ts
+++ b/e2e/fixtures/agent-prompt-cache/evals/evals.config.ts
@@ -2,5 +2,5 @@ import { defineEvalConfig } from "eve/evals";
 
 /** Judge is unused here; assertions are numeric. Kept for config parity. */
 export default defineEvalConfig({
-  judge: { model: "openai/gpt-5.5" },
+  judge: { model: "openai/gpt-5.6-sol" },
 });
diff --git a/e2e/fixtures/agent-schedules/agent/agent.ts b/e2e/fixtures/agent-schedules/agent/agent.ts
index dc6d957f5..7c4adca2c 100644
--- a/e2e/fixtures/agent-schedules/agent/agent.ts
+++ b/e2e/fixtures/agent-schedules/agent/agent.ts
@@ -1,6 +1,6 @@
 import { defineAgent } from "eve";
 
 export default defineAgent({
-  model: "anthropic/claude-sonnet-5",
+  model: "openai/gpt-5.6-sol",
   reasoning: "high",
 });
diff --git a/e2e/fixtures/agent-schedules/evals/evals.config.ts b/e2e/fixtures/agent-schedules/evals/evals.config.ts
index 6864dd176..912e6ec89 100644
--- a/e2e/fixtures/agent-schedules/evals/evals.config.ts
+++ b/e2e/fixtures/agent-schedules/evals/evals.config.ts
@@ -2,5 +2,5 @@ import { defineEvalConfig } from "eve/evals";
 
 /** Default judge model for any `t.judge.*` assertion in this fixture. */
 export default defineEvalConfig({
-  judge: { model: "openai/gpt-5.5" },
+  judge: { model: "openai/gpt-5.6-sol" },
 });
diff --git a/e2e/fixtures/agent-session-limits/agent/agent.ts b/e2e/fixtures/agent-session-limits/agent/agent.ts
index 1270e5255..c8b87b74d 100644
--- a/e2e/fixtures/agent-session-limits/agent/agent.ts
+++ b/e2e/fixtures/agent-session-limits/agent/agent.ts
@@ -1,7 +1,7 @@
 import { defineAgent } from "eve";
 
 export default defineAgent({
-  model: "anthropic/claude-sonnet-5",
+  model: "openai/gpt-5.6-sol",
   // A one-token input budget guarantees every completed model call crosses
   // the limit, so the next conversation turn deterministically parks on the
   // session-limit continuation prompt.
diff --git a/e2e/fixtures/agent-session-limits/evals/evals.config.ts b/e2e/fixtures/agent-session-limits/evals/evals.config.ts
index 6864dd176..912e6ec89 100644
--- a/e2e/fixtures/agent-session-limits/evals/evals.config.ts
+++ b/e2e/fixtures/agent-session-limits/evals/evals.config.ts
@@ -2,5 +2,5 @@ import { defineEvalConfig } from "eve/evals";
 
 /** Default judge model for any `t.judge.*` assertion in this fixture. */
 export default defineEvalConfig({
-  judge: { model: "openai/gpt-5.5" },
+  judge: { model: "openai/gpt-5.6-sol" },
 });
diff --git a/e2e/fixtures/agent-skills/agent/agent.ts b/e2e/fixtures/agent-skills/agent/agent.ts
index dc6d957f5..7c4adca2c 100644
--- a/e2e/fixtures/agent-skills/agent/agent.ts
+++ b/e2e/fixtures/agent-skills/agent/agent.ts
@@ -1,6 +1,6 @@
 import { defineAgent } from "eve";
 
 export default defineAgent({
-  model: "anthropic/claude-sonnet-5",
+  model: "openai/gpt-5.6-sol",
   reasoning: "high",
 });
diff --git a/e2e/fixtures/agent-skills/evals/evals.config.ts b/e2e/fixtures/agent-skills/evals/evals.config.ts
index 6864dd176..912e6ec89 100644
--- a/e2e/fixtures/agent-skills/evals/evals.config.ts
+++ b/e2e/fixtures/agent-skills/evals/evals.config.ts
@@ -2,5 +2,5 @@ import { defineEvalConfig } from "eve/evals";
 
 /** Default judge model for any `t.judge.*` assertion in this fixture. */
 export default defineEvalConfig({
-  judge: { model: "openai/gpt-5.5" },
+  judge: { model: "openai/gpt-5.6-sol" },
 });
diff --git a/e2e/fixtures/agent-subagents-hitl/agent/agent.ts b/e2e/fixtures/agent-subagents-hitl/agent/agent.ts
index dc6d957f5..7c4adca2c 100644
--- a/e2e/fixtures/agent-subagents-hitl/agent/agent.ts
+++ b/e2e/fixtures/agent-subagents-hitl/agent/agent.ts
@@ -1,6 +1,6 @@
 import { defineAgent } from "eve";
 
 export default defineAgent({
-  model: "anthropic/claude-sonnet-5",
+  model: "openai/gpt-5.6-sol",
   reasoning: "high",
 });
diff --git a/e2e/fixtures/agent-subagents-hitl/agent/subagents/stock-price/agent.ts b/e2e/fixtures/agent-subagents-hitl/agent/subagents/stock-price/agent.ts
index 10007be3a..0a1a56d1f 100644
--- a/e2e/fixtures/agent-subagents-hitl/agent/subagents/stock-price/agent.ts
+++ b/e2e/fixtures/agent-subagents-hitl/agent/subagents/stock-price/agent.ts
@@ -3,6 +3,6 @@ import { defineAgent } from "eve";
 export default defineAgent({
   description:
     'Look up the current stock price for a given ticker symbol. Pass the ticker symbol you want to look up in the message (e.g. "AAPL", "GOOG", or "TSLA").',
-  model: "anthropic/claude-sonnet-5",
+  model: "openai/gpt-5.6-sol",
   reasoning: "high",
 });
diff --git a/e2e/fixtures/agent-subagents-hitl/evals/evals.config.ts b/e2e/fixtures/agent-subagents-hitl/evals/evals.config.ts
index 6864dd176..912e6ec89 100644
--- a/e2e/fixtures/agent-subagents-hitl/evals/evals.config.ts
+++ b/e2e/fixtures/agent-subagents-hitl/evals/evals.config.ts
@@ -2,5 +2,5 @@ import { defineEvalConfig } from "eve/evals";
 
 /** Default judge model for any `t.judge.*` assertion in this fixture. */
 export default defineEvalConfig({
-  judge: { model: "openai/gpt-5.5" },
+  judge: { model: "openai/gpt-5.6-sol" },
 });
diff --git a/e2e/fixtures/agent-subagents/agent/agent.ts b/e2e/fixtures/agent-subagents/agent/agent.ts
index dc6d957f5..7c4adca2c 100644
--- a/e2e/fixtures/agent-subagents/agent/agent.ts
+++ b/e2e/fixtures/agent-subagents/agent/agent.ts
@@ -1,6 +1,6 @@
 import { defineAgent } from "eve";
 
 export default defineAgent({
-  model: "anthropic/claude-sonnet-5",
+  model: "openai/gpt-5.6-sol",
   reasoning: "high",
 });
diff --git a/e2e/fixtures/agent-subagents/agent/subagents/echo-marker/agent.ts b/e2e/fixtures/agent-subagents/agent/subagents/echo-marker/agent.ts
index 1e5c462e5..3084a65fb 100644
--- a/e2e/fixtures/agent-subagents/agent/subagents/echo-marker/agent.ts
+++ b/e2e/fixtures/agent-subagents/agent/subagents/echo-marker/agent.ts
@@ -12,6 +12,6 @@ import { defineAgent } from "eve";
 export default defineAgent({
   description:
     "Smoke-test echo subagent. Call this whenever the user mentions the phrase 'echo marker subagent'. Pass any short text as the input; the subagent replies with a fixed marker token.",
-  model: "anthropic/claude-sonnet-5",
+  model: "openai/gpt-5.6-sol",
   reasoning: "high",
 });
diff --git a/e2e/fixtures/agent-subagents/evals/evals.config.ts b/e2e/fixtures/agent-subagents/evals/evals.config.ts
index 6864dd176..912e6ec89 100644
--- a/e2e/fixtures/agent-subagents/evals/evals.config.ts
+++ b/e2e/fixtures/agent-subagents/evals/evals.config.ts
@@ -2,5 +2,5 @@ import { defineEvalConfig } from "eve/evals";
 
 /** Default judge model for any `t.judge.*` assertion in this fixture. */
 export default defineEvalConfig({
-  judge: { model: "openai/gpt-5.5" },
+  judge: { model: "openai/gpt-5.6-sol" },
 });
diff --git a/e2e/fixtures/agent-tools-hitl-openai/agent/agent.ts b/e2e/fixtures/agent-tools-hitl-openai/agent/agent.ts
index a780c41c4..99a9c1f72 100644
--- a/e2e/fixtures/agent-tools-hitl-openai/agent/agent.ts
+++ b/e2e/fixtures/agent-tools-hitl-openai/agent/agent.ts
@@ -7,5 +7,5 @@ import { defineAgent } from "eve";
  * validated by OpenAI's `function_call` / `function_call_output` pairing.
  */
 export default defineAgent({
-  model: "openai/gpt-5.5",
+  model: "openai/gpt-5.6-sol",
 });
diff --git a/e2e/fixtures/agent-tools-hitl-openai/evals/evals.config.ts b/e2e/fixtures/agent-tools-hitl-openai/evals/evals.config.ts
index 6864dd176..912e6ec89 100644
--- a/e2e/fixtures/agent-tools-hitl-openai/evals/evals.config.ts
+++ b/e2e/fixtures/agent-tools-hitl-openai/evals/evals.config.ts
@@ -2,5 +2,5 @@ import { defineEvalConfig } from "eve/evals";
 
 /** Default judge model for any `t.judge.*` assertion in this fixture. */
 export default defineEvalConfig({
-  judge: { model: "openai/gpt-5.5" },
+  judge: { model: "openai/gpt-5.6-sol" },
 });
diff --git a/e2e/fixtures/agent-tools-hitl/agent/agent.ts b/e2e/fixtures/agent-tools-hitl/agent/agent.ts
index dc6d957f5..7c4adca2c 100644
--- a/e2e/fixtures/agent-tools-hitl/agent/agent.ts
+++ b/e2e/fixtures/agent-tools-hitl/agent/agent.ts
@@ -1,6 +1,6 @@
 import { defineAgent } from "eve";
 
 export default defineAgent({
-  model: "anthropic/claude-sonnet-5",
+  model: "openai/gpt-5.6-sol",
   reasoning: "high",
 });
diff --git a/e2e/fixtures/agent-tools-hitl/evals/evals.config.ts b/e2e/fixtures/agent-tools-hitl/evals/evals.config.ts
index 6864dd176..912e6ec89 100644
--- a/e2e/fixtures/agent-tools-hitl/evals/evals.config.ts
+++ b/e2e/fixtures/agent-tools-hitl/evals/evals.config.ts
@@ -2,5 +2,5 @@ import { defineEvalConfig } from "eve/evals";
 
 /** Default judge model for any `t.judge.*` assertion in this fixture. */
 export default defineEvalConfig({
-  judge: { model: "openai/gpt-5.5" },
+  judge: { model: "openai/gpt-5.6-sol" },
 });
diff --git a/e2e/fixtures/agent-tools-sandbox/agent/agent.ts b/e2e/fixtures/agent-tools-sandbox/agent/agent.ts
index dc6d957f5..7c4adca2c 100644
--- a/e2e/fixtures/agent-tools-sandbox/agent/agent.ts
+++ b/e2e/fixtures/agent-tools-sandbox/agent/agent.ts
@@ -1,6 +1,6 @@
 import { defineAgent } from "eve";
 
 export default defineAgent({
-  model: "anthropic/claude-sonnet-5",
+  model: "openai/gpt-5.6-sol",
   reasoning: "high",
 });
diff --git a/e2e/fixtures/agent-tools-sandbox/evals/evals.config.ts b/e2e/fixtures/agent-tools-sandbox/evals/evals.config.ts
index 6864dd176..912e6ec89 100644
--- a/e2e/fixtures/agent-tools-sandbox/evals/evals.config.ts
+++ b/e2e/fixtures/agent-tools-sandbox/evals/evals.config.ts
@@ -2,5 +2,5 @@ import { defineEvalConfig } from "eve/evals";
 
 /** Default judge model for any `t.judge.*` assertion in this fixture. */
 export default defineEvalConfig({
-  judge: { model: "openai/gpt-5.5" },
+  judge: { model: "openai/gpt-5.6-sol" },
 });
diff --git a/e2e/fixtures/agent-tools/agent/agent.ts b/e2e/fixtures/agent-tools/agent/agent.ts
index dc6d957f5..7c4adca2c 100644
--- a/e2e/fixtures/agent-tools/agent/agent.ts
+++ b/e2e/fixtures/agent-tools/agent/agent.ts
@@ -1,6 +1,6 @@
 import { defineAgent } from "eve";
 
 export default defineAgent({
-  model: "anthropic/claude-sonnet-5",
+  model: "openai/gpt-5.6-sol",
   reasoning: "high",
 });
diff --git a/e2e/fixtures/agent-tools/evals/evals.config.ts b/e2e/fixtures/agent-tools/evals/evals.config.ts
index 6864dd176..912e6ec89 100644
--- a/e2e/fixtures/agent-tools/evals/evals.config.ts
+++ b/e2e/fixtures/agent-tools/evals/evals.config.ts
@@ -2,5 +2,5 @@ import { defineEvalConfig } from "eve/evals";
 
 /** Default judge model for any `t.judge.*` assertion in this fixture. */
 export default defineEvalConfig({
-  judge: { model: "openai/gpt-5.5" },
+  judge: { model: "openai/gpt-5.6-sol" },
 });
diff --git a/e2e/fixtures/extensions/agent/agent.ts b/e2e/fixtures/extensions/agent/agent.ts
index dc6d957f5..7c4adca2c 100644
--- a/e2e/fixtures/extensions/agent/agent.ts
+++ b/e2e/fixtures/extensions/agent/agent.ts
@@ -1,6 +1,6 @@
 import { defineAgent } from "eve";
 
 export default defineAgent({
-  model: "anthropic/claude-sonnet-5",
+  model: "openai/gpt-5.6-sol",
   reasoning: "high",
 });
diff --git a/e2e/fixtures/extensions/evals/evals.config.ts b/e2e/fixtures/extensions/evals/evals.config.ts
index 8102d33af..292229fa1 100644
--- a/e2e/fixtures/extensions/evals/evals.config.ts
+++ b/e2e/fixtures/extensions/evals/evals.config.ts
@@ -1,5 +1,5 @@
 import { defineEvalConfig } from "eve/evals";
 
 export default defineEvalConfig({
-  judge: { model: "openai/gpt-5.5" },
+  judge: { model: "openai/gpt-5.6-sol" },
 });