feat: add compaction model override for session compaction operations

Adds a dedicated compaction model selector so users can run one model
for chat and a different model for summarization (e.g. Claude Sonnet for
interactive coding, Zen Big Pickle free tier for zero-cost compaction).

Model resolution priority: TUI selection > agent.compaction.model config
> session model. When no TUI selection is set, behavior is identical to
upstream.

Changes:
- DialogModel gains target="compaction" prop — no duplicate component
- SessionCompaction.process() accepts optional compactionModel override
- CompactionPart schema extended with optional compactionModel field
- compaction_model_list keybind added (default: none)
- /compaction-models slash command and command menu entry
- local.model.compaction context backed by kv.signal('compaction_model')
- Prompt footer shows active compaction model when set
- SDK regenerated via ./script/generate.ts

Author: ryanwyler

packages/opencode/src/cli/cmd/tui/app.tsx

@@ -445,6 +445,20 @@ function App() {
         local.model.cycleFavorite(-1)
       },
     },
+    {
+      title: "Switch compaction model",
+      value: "compaction_model.list",
+      keybind: "compaction_model_list",
+      category: "Agent",
+      slash: {
+        name: "compaction-models",
+        aliases: ["compaction-model"],
+      },
+      onSelect: () => {
+        dialog.replace(() => <DialogModel target="compaction" />)
+      },
+    },
+
     {
       title: "Switch agent",
       value: "agent.list",

packages/opencode/src/cli/cmd/tui/component/dialog-model.tsx

@@ -15,7 +15,7 @@ export function useConnected() {
   )
 }
 
-export function DialogModel(props: { providerID?: string }) {
+export function DialogModel(props: { providerID?: string; target?: "session" | "compaction" }) {
   const local = useLocal()
   const sync = useSync()
   const dialog = useDialog()
@@ -25,14 +25,41 @@ export function DialogModel(props: { providerID?: string }) {
   const connected = useConnected()
   const providers = createDialogProviderOptions()
 
+  const isCompaction = props.target === "compaction"
+
   const showExtra = createMemo(() => connected() && !props.providerID)
 
+  function onModelSelect(model: { providerID: string; modelID: string }) {
+    dialog.clear()
+    if (isCompaction) {
+      local.model.compaction.set(model)
+      return
+    }
+    local.model.set(model, { recent: true })
+  }
+
   const options = createMemo(() => {
     const needle = query().trim()
     const showSections = showExtra() && needle.length === 0
     const favorites = connected() ? local.model.favorite() : []
     const recents = local.model.recent()
 
+    // "Use session model (default)" option only shown in compaction mode
+    const defaultOption = isCompaction
+      ? [
+          {
+            value: { providerID: "", modelID: "" },
+            title: "Use session model (default)",
+            description: "Compaction will use the same model as the session",
+            category: showSections ? "Default" : undefined,
+            onSelect: () => {
+              dialog.clear()
+              local.model.compaction.clear()
+            },
+          },
+        ]
+      : []
+
     function toOptions(items: typeof favorites, category: string) {
       if (!showSections) return []
       return items.flatMap((item) => {
@@ -49,10 +76,7 @@ export function DialogModel(props: { providerID?: string }) {
             category,
             disabled: provider.id === "opencode" && model.id.includes("-nano"),
             footer: model.cost?.input === 0 && provider.id === "opencode" ? "Free" : undefined,
-            onSelect: () => {
-              dialog.clear()
-              local.model.set({ providerID: provider.id, modelID: model.id }, { recent: true })
-            },
+            onSelect: () => onModelSelect({ providerID: provider.id, modelID: model.id }),
           },
         ]
       })
@@ -87,10 +111,7 @@ export function DialogModel(props: { providerID?: string }) {
             category: connected() ? provider.name : undefined,
             disabled: provider.id === "opencode" && model.includes("-nano"),
             footer: info.cost?.input === 0 && provider.id === "opencode" ? "Free" : undefined,
-            onSelect() {
-              dialog.clear()
-              local.model.set({ providerID: provider.id, modelID: model }, { recent: true })
-            },
+            onSelect: () => onModelSelect({ providerID: provider.id, modelID: model }),
           })),
           filter((x) => {
             if (!showSections) return true
@@ -121,19 +142,22 @@ export function DialogModel(props: { providerID?: string }) {
 
     if (needle) {
       return [
+        ...defaultOption,
         ...fuzzysort.go(needle, providerOptions, { keys: ["title", "category"] }).map((x) => x.obj),
         ...fuzzysort.go(needle, popularProviders, { keys: ["title"] }).map((x) => x.obj),
       ]
     }
 
-    return [...favoriteOptions, ...recentOptions, ...providerOptions, ...popularProviders]
+    return [...defaultOption, ...favoriteOptions, ...recentOptions, ...providerOptions, ...popularProviders]
   })
 
   const provider = createMemo(() =>
     props.providerID ? sync.data.provider.find((x) => x.id === props.providerID) : null,
   )
 
-  const title = createMemo(() => provider()?.name ?? "Select model")
+  const title = createMemo(() => (isCompaction ? "Select compaction model" : (provider()?.name ?? "Select model")))
+
+  const current = createMemo(() => (isCompaction ? local.model.compaction.current() : local.model.current()))
 
   return (
     <DialogSelect<ReturnType<typeof options>[number]["value"]>
@@ -151,15 +175,18 @@ export function DialogModel(props: { providerID?: string }) {
           title: "Favorite",
           disabled: !connected(),
           onTrigger: (option) => {
-            local.model.toggleFavorite(option.value as { providerID: string; modelID: string })
+            const val = option.value as { providerID: string; modelID: string }
+            if (val.providerID && val.modelID) {
+              local.model.toggleFavorite(val)
+            }
           },
         },
       ]}
       onFilter={setQuery}
       flat={true}
       skipFilter={true}
       title={title()}
-      current={local.model.current()}
+      current={current()}
     />
   )
 }

packages/opencode/src/cli/cmd/tui/component/prompt/index.tsx

@@ -1012,6 +1012,10 @@ export function Prompt(props: PromptProps) {
                       <span style={{ fg: theme.warning, bold: true }}>{local.model.variant.current()}</span>
                     </text>
                   </Show>
+                  <Show when={local.model.compaction.current()}>
+                    <text fg={theme.textMuted}>·</text>
+                    <text fg={theme.textMuted}>compact: {local.model.compaction.parsed().model}</text>
+                  </Show>
                 </box>
               </Show>
             </box>

packages/opencode/src/cli/cmd/tui/context/local.tsx

@@ -13,13 +13,15 @@ import { useArgs } from "./args"
 import { useSDK } from "./sdk"
 import { RGBA } from "@opentui/core"
 import { Filesystem } from "@/util/filesystem"
+import { useKV } from "./kv"
 
 export const { use: useLocal, provider: LocalProvider } = createSimpleContext({
   name: "Local",
   init: () => {
     const sync = useSync()
     const sdk = useSDK()
     const toast = useToast()
+    const kv = useKV()
 
     function isModelValid(model: { providerID: string; modelID: string }) {
       const provider = sync.data.provider.find((x) => x.id === model.providerID)
@@ -320,6 +322,44 @@ export const { use: useLocal, provider: LocalProvider } = createSimpleContext({
             save()
           })
         },
+        compaction: iife(() => {
+          const key = "compaction_model"
+          const [get] = kv.signal<{ providerID: string; modelID: string } | undefined>(key, undefined)
+          return {
+            current() {
+              return get() as { providerID: string; modelID: string } | undefined
+            },
+            parsed: createMemo(() => {
+              const value = get() as { providerID: string; modelID: string } | undefined
+              if (!value) {
+                return {
+                  provider: undefined,
+                  model: "Using session model",
+                }
+              }
+              const provider = sync.data.provider.find((x) => x.id === value.providerID)
+              const info = provider?.models[value.modelID]
+              return {
+                provider: provider?.name ?? value.providerID,
+                model: info?.name ?? value.modelID,
+              }
+            }),
+            set(model: { providerID: string; modelID: string }) {
+              if (!isModelValid(model)) {
+                toast.show({
+                  message: `Model ${model.providerID}/${model.modelID} is not valid`,
+                  variant: "warning",
+                  duration: 3000,
+                })
+                return
+              }
+              kv.set(key, { ...model })
+            },
+            clear() {
+              kv.set(key, undefined)
+            },
+          }
+        }),
         variant: {
           current() {
             const m = currentModel()

packages/opencode/src/cli/cmd/tui/routes/session/index.tsx

@@ -461,10 +461,12 @@ export function Session() {
           })
           return
         }
+        const compactionModel = local.model.compaction.current()
         sdk.client.session.summarize({
           sessionID: route.sessionID,
           modelID: selectedModel.modelID,
           providerID: selectedModel.providerID,
+          compactionModel: compactionModel ?? undefined,
         })
         dialog.clear()
       },

packages/opencode/src/config/config.ts

@@ -809,6 +809,7 @@ export namespace Config {
       model_cycle_recent_reverse: z.string().optional().default("shift+f2").describe("Previous recently used model"),
       model_cycle_favorite: z.string().optional().default("none").describe("Next favorite model"),
       model_cycle_favorite_reverse: z.string().optional().default("none").describe("Previous favorite model"),
+      compaction_model_list: z.string().optional().default("none").describe("List available compaction models"),
       command_list: z.string().optional().default("ctrl+p").describe("List available commands"),
       agent_list: z.string().optional().default("<leader>a").describe("List agents"),
       agent_cycle: z.string().optional().default("tab").describe("Next agent"),

packages/opencode/src/server/routes/session.ts

@@ -17,7 +17,7 @@ import { Log } from "../../util/log"
 import { PermissionNext } from "@/permission/next"
 import { errors } from "../error"
 import { lazy } from "../../util/lazy"
-import { SessionProxyMiddleware } from "../../control-plane/session-proxy-middleware"
+
 import { Config } from "../../config/config"
 
 const log = Log.create({ service: "server" })
@@ -564,6 +564,12 @@ export const SessionRoutes = lazy(() =>
           providerID: z.string(),
           modelID: z.string(),
           auto: z.boolean().optional().default(false),
+          compactionModel: z
+            .object({
+              providerID: z.string(),
+              modelID: z.string(),
+            })
+            .optional(),
         }),
       ),
       async (c) => {
@@ -588,6 +594,7 @@ export const SessionRoutes = lazy(() =>
             modelID: body.modelID,
           },
           auto: body.auto,
+          compactionModel: body.compactionModel,
         })
         await SessionPrompt.loop({ sessionID })
         return c.json(true)

packages/opencode/src/session/compaction-extension.ts

@@ -184,6 +184,8 @@ Critical rules:
     sessionID: string
     abort: AbortSignal
     auto: boolean
+    compactionModel?: { providerID: string; modelID: string }
+    overflow?: boolean
   }): Promise<"continue" | "stop"> {
     const config = await Config.get()
     const extractRatio = config.compaction?.extractRatio ?? DEFAULTS.extractRatio
@@ -206,9 +208,12 @@ Critical rules:
     // Get the user message to determine which model we'll use
     const originalUserMessage = input.messages.findLast((m) => m.info.id === input.parentID)!.info as MessageV2.User
     const agent = await Agent.get("compaction")
-    const model = agent.model
-      ? await Provider.getModel(agent.model.providerID, agent.model.modelID)
-      : await Provider.getModel(originalUserMessage.model.providerID, originalUserMessage.model.modelID)
+    // Model resolution priority: TUI compactionModel override > agent.compaction.model config > session model
+    const model = input.compactionModel
+      ? await Provider.getModel(input.compactionModel.providerID, input.compactionModel.modelID)
+      : agent.model
+        ? await Provider.getModel(agent.model.providerID, agent.model.modelID)
+        : await Provider.getModel(originalUserMessage.model.providerID, originalUserMessage.model.modelID)
 
     // Calculate token counts and role counts
     let messageTokens: number[] = []

packages/opencode/src/session/compaction.ts

@@ -108,6 +108,7 @@ export namespace SessionCompaction {
 
   export async function process(input: {
     parentID: string
+    compactionModel?: { providerID: string; modelID: string }
     messages: MessageV2.WithParts[]
     sessionID: string
     abort: AbortSignal
@@ -175,9 +176,11 @@ export namespace SessionCompaction {
     }
 
     const agent = await Agent.get("compaction")
-    const model = agent.model
-      ? await Provider.getModel(agent.model.providerID, agent.model.modelID)
-      : await Provider.getModel(userMessage.model.providerID, userMessage.model.modelID)
+    const model = input.compactionModel
+      ? await Provider.getModel(input.compactionModel.providerID, input.compactionModel.modelID)
+      : agent.model
+        ? await Provider.getModel(agent.model.providerID, agent.model.modelID)
+        : await Provider.getModel(userMessage.model.providerID, userMessage.model.modelID)
     const msg = (await Session.updateMessage({
       id: Identifier.ascending("message"),
       role: "assistant",
@@ -349,6 +352,12 @@ When constructing the summary, try to stick to this template:
       }),
       auto: z.boolean(),
       overflow: z.boolean().optional(),
+      compactionModel: z
+        .object({
+          providerID: z.string(),
+          modelID: z.string(),
+        })
+        .optional(),
     }),
     async (input) => {
       const msg = await Session.updateMessage({
@@ -368,6 +377,7 @@ When constructing the summary, try to stick to this template:
         type: "compaction",
         auto: input.auto,
         overflow: input.overflow,
+        compactionModel: input.compactionModel,
       })
     },
   )

packages/opencode/src/session/message-v2.ts

@@ -204,6 +204,12 @@ export namespace MessageV2 {
     type: z.literal("compaction"),
     auto: z.boolean(),
     overflow: z.boolean().optional(),
+    compactionModel: z
+      .object({
+        providerID: z.string(),
+        modelID: z.string(),
+      })
+      .optional(),
   }).meta({
     ref: "CompactionPart",
   })
@@ -875,7 +881,7 @@ export namespace MessageV2 {
       // Upstream guard: do not mark errored summaries as completed breakpoints.
       // Collapse compaction may not set finish, but summary: true is sufficient;
       // however an errored summary must not be treated as a valid breakpoint.
-      if (isAssistantSummary && !msg.info.error) {
+      if (isAssistantSummary && !(msg.info as Assistant).error) {
         const parentID = (msg.info as Assistant).parentID
         log.debug("COLLAPSE filterCompacted found summary", {
           msgId: msg.info.id,