diff --git a/packages/core/src/session/compaction.ts b/packages/core/src/session/compaction.ts
index f1103d0c3a..ce4e84e91f 100644
--- a/packages/core/src/session/compaction.ts
+++ b/packages/core/src/session/compaction.ts
@@ -80,24 +80,25 @@ export interface Interface {
 
 export class Service extends Context.Service<Service, Interface>()("@opencode/v2/SessionCompaction") {}
 
-const estimate = (value: unknown) => Token.estimate(JSON.stringify(value))
+const stringify = (value: unknown) => (typeof value === "string" ? value : (JSON.stringify(value) ?? String(value)))
 
-const textContext = (request: LLMRequest) => ({
-  system: request.system,
-  // TODO: Replace media exclusion with model-aware attachment token accounting.
-  messages: request.messages.map((message) => ({
-    id: message.id,
-    role: message.role,
-    content: message.content.flatMap((part) => {
-      if (part.type === "media") return []
-      if (part.type !== "tool-result" || part.result.type !== "content") return [part]
-      return [{ ...part, result: { ...part.result, value: part.result.value.filter((item) => item.type === "text") } }]
-    }),
-    metadata: message.metadata,
-    native: message.native,
-  })),
-  tools: request.tools,
-})
+const serializeContent = (part: LLMRequest["messages"][number]["content"][number]) => {
+  if (part.type === "text" || part.type === "reasoning") return part.text
+  if (part.type === "media") return ""
+  if (part.type === "tool-call") return `${part.name}\n${stringify(part.input)}`
+  if (part.result.type === "content")
+    return [part.name, ...part.result.value.flatMap((item) => (item.type === "text" ? [item.text] : []))].join("\n")
+  return `${part.name}\n${stringify(part.result.value)}`
+}
+
+const estimate = (request: LLMRequest) =>
+  Token.estimate(
+    [
+      ...request.system.map((part) => part.text),
+      JSON.stringify(request.tools),
+      ...request.messages.flatMap((message) => message.content.map(serializeContent).filter(Boolean)),
+    ].join("\n"),
+  )
 
 const truncate = (value: string) =>
   value.length <= TOOL_OUTPUT_MAX_CHARS ? value : `${value.slice(0, TOOL_OUTPUT_MAX_CHARS)}\n[truncated]`
@@ -302,7 +303,7 @@ const make = (dependencies: Dependencies) => {
     const context = input.request.model.route.defaults.limits?.context
     if (context === undefined || context <= 0) return false
     const output = input.request.generation?.maxTokens ?? input.request.model.route.defaults.limits?.output ?? 0
-    if (estimate(textContext(input.request)) <= context - Math.max(output, config.buffer)) return false
+    if (estimate(input.request) <= context - Math.max(output, config.buffer)) return false
     return yield* compactAfterOverflow(input)
   })
   return {
diff --git a/packages/core/test/session-compaction.test.ts b/packages/core/test/session-compaction.test.ts
index 0f9f8e12ec..ae6c1c70a8 100644
--- a/packages/core/test/session-compaction.test.ts
+++ b/packages/core/test/session-compaction.test.ts
@@ -1,5 +1,5 @@
 import { expect, test } from "bun:test"
-import { LLM, LLMClient, LLMEvent, Model, type LLMRequest } from "@opencode-ai/llm"
+import { LLM, LLMClient, LLMEvent, Message, Model, ToolCallPart, type LLMRequest } from "@opencode-ai/llm"
 import { OpenAIChat } from "@opencode-ai/llm/protocols"
 import { Base64, FileAttachment } from "@opencode-ai/schema/prompt"
 import { Config } from "@opencode-ai/core/config"
@@ -131,6 +131,68 @@ it.effect("does not count image attachments as text context", () =>
   }),
 )
 
+it.effect("counts tool-call inputs as text context", () =>
+  Effect.gen(function* () {
+    requests = []
+    const db = (yield* Database.Service).db
+    const compaction = yield* SessionCompaction.Service
+    const text = "context ".repeat(4_500)
+    const sessionID = SessionV2.ID.make("ses_tool_input_compaction")
+    const inputModel = Model.make({
+      id: "tool-input-model",
+      provider: "test",
+      route: OpenAIChat.route.with({ limits: { context: 30_000, output: 1_000 } }),
+    })
+    const messages = [
+      SessionMessage.User.make({
+        id: SessionMessage.ID.create(),
+        type: "user",
+        text,
+        time: { created: DateTime.makeUnsafe(0) },
+      }),
+      SessionMessage.User.make({
+        id: SessionMessage.ID.create(),
+        type: "user",
+        text: "Continue",
+        time: { created: DateTime.makeUnsafe(1) },
+      }),
+    ]
+    yield* db
+      .insert(ProjectTable)
+      .values({ id: Project.ID.global, worktree: AbsolutePath.make("/project"), sandboxes: [] })
+      .onConflictDoNothing()
+      .run()
+      .pipe(Effect.orDie)
+    yield* db
+      .insert(SessionTable)
+      .values({
+        id: sessionID,
+        project_id: Project.ID.global,
+        slug: "tool-input-compaction",
+        directory: "/project",
+        title: "Tool input compaction",
+        version: "test",
+      })
+      .run()
+      .pipe(Effect.orDie)
+
+    expect(
+      yield* compaction.compactIfNeeded({
+        sessionID,
+        messages,
+        request: LLM.request({
+          model: inputModel,
+          messages: [
+            Message.user(text),
+            Message.assistant(ToolCallPart.make({ id: "call_read", name: "read", input: { path: "x".repeat(8_000) } })),
+          ],
+        }),
+      }),
+    ).toBe(true)
+    expect(requests).toHaveLength(1)
+  }),
+)
+
 test("compaction prompt requires the checkpoint headings in order", () => {
   const prompt = SessionCompaction.buildPrompt({ context: ["Conversation history"] })
   expect(prompt.match(/^#{2,3} .+$/gm)).toEqual([