diff --git a/packages/extension/src/opencode_config.ts b/packages/extension/src/opencode_config.ts
index b6631082..e3468c16 100644
--- a/packages/extension/src/opencode_config.ts
+++ b/packages/extension/src/opencode_config.ts
@@ -37,10 +37,11 @@ export function resolveJuliaProject(configValue: string): string {
 }
 
 /** Build the OPENCODE_CONFIG_CONTENT value: a config object that injects the
- *  amico AGENTS.md as a top-level `instructions` entry AND auto-allows the
+ *  amico AGENTS.md as a top-level `instructions` entry, PINS the team model
+ *  (AMICODE_MODEL — never the user's global model), and auto-allows the
  *  permissions the solve workflow needs. opencode MERGES this over the user's
- *  global config (model/provider preserved) for every session, independent of
- *  the session's working directory.
+ *  global config (non-conflicting user keys preserved) for every session,
+ *  independent of the session's working directory.
  *
  *  Why the `permission` block: the agent reads the bundled template at an
  *  absolute path *outside* the session's working dir and writes scratch to
@@ -71,10 +72,21 @@ export function resolveJuliaProject(configValue: string): string {
  *  `webfetch` is intentionally NOT set — the solve flow never fetches a URL. */
 const SCRATCH_DIR = "/tmp/amicode-work";   // matches AGENTS.md step 2/3
 
+/** The ONE model every amicode session runs — pinned, never read from the
+ *  user's global opencode config. Rationale: sessions were silently falling
+ *  back to opencode's free anonymous model (`big-pickle`) on machines with an
+ *  empty global config, which is exactly the "free-model phrasing variance"
+ *  behind protocol breaks (invented Other options, JSON drift) — and two
+ *  teammates debugging the same interview must be running the same model.
+ *  Requires provider auth (`opencode auth login`); with none, sessions fail
+ *  loudly instead of silently degrading. */
+export const AMICODE_MODEL = "anthropic/claude-sonnet-5";
+
 export function buildOpencodeConfigContent(agentsPath: string, templatePath: string, runsRoot: string): string {
   const templatesDir = path.dirname(templatePath);
   return JSON.stringify({
     $schema: "https://opencode.ai/config.json",
+    model: AMICODE_MODEL,   // pinned team-wide — overrides any user global model (deep-merge, ours wins)
     instructions: [agentsPath],
     permission: {
       bash: "allow",
diff --git a/packages/extension/test/opencode_config.test.ts b/packages/extension/test/opencode_config.test.ts
index f1961796..997a3570 100644
--- a/packages/extension/test/opencode_config.test.ts
+++ b/packages/extension/test/opencode_config.test.ts
@@ -3,7 +3,7 @@ import { existsSync, mkdtempSync, mkdirSync, writeFileSync, readFileSync } from
 import { tmpdir, homedir } from 'node:os'
 import { join } from 'node:path'
 import { execFileSync } from 'node:child_process'
-import { prepareOpencodeProject, resolveJuliaProject, buildOpencodeConfigContent } from '../src/opencode_config'
+import { prepareOpencodeProject, resolveJuliaProject, buildOpencodeConfigContent, AMICODE_MODEL } from '../src/opencode_config'
 
 function fakeExtRoot(): string {
   const root = mkdtempSync(join(tmpdir(), 'extroot-'))
@@ -87,11 +87,12 @@ describe('buildOpencodeConfigContent', () => {
 // binary isn't present (e.g. minimal CI before `fetch:opencode`).
 const OC_BIN = join(__dirname, '..', 'vendor', 'opencode', `${process.platform}-${process.arch}`, 'opencode')
 describe.skipIf(!existsSync(OC_BIN))('opencode config injection + merge (1.17.3)', () => {
-  it('injects instructions/permission AND preserves the user global model + permission', () => {
+  it('injects instructions/permission, PINS the team model over the user global, preserves other user keys', () => {
     const home = mkdtempSync(join(tmpdir(), 'ochome-'))
     mkdirSync(join(home, '.config', 'opencode'), { recursive: true })
-    // A user global config with a distinctive model + permission key — both must
-    // survive the deep-merge under OPENCODE_CONFIG_CONTENT.
+    // A user global config with a CONFLICTING model + a distinctive permission
+    // key: the model must LOSE to the pin (one team, one model — no silent
+    // big-pickle fallback, no per-machine drift); the permission key must survive.
     writeFileSync(join(home, '.config', 'opencode', 'opencode.json'),
       JSON.stringify({ model: 'anthropic/claude-sonnet-4-6', permission: { doom_loop: 'deny' } }))
     const agentsPath = join(home, 'AGENTS.md')   // the exact file our `instructions` must point at
@@ -108,8 +109,9 @@ describe.skipIf(!existsSync(OC_BIN))('opencode config injection + merge (1.17.3)
     // the runs-root grant survives the real deep-merge — the agent's post-solve
     // FINISHED/result.toml/run.log read-backs must not "ask" on every run:
     expect(cfg.permission.external_directory[join(home, '.amico', 'runs', 'default') + '/**']).toBe('allow')
-    // the user's global config SURVIVED the deep-merge:
-    expect(cfg.model).toBe('anthropic/claude-sonnet-4-6')          // provider/model preserved (Q129 needs this)
+    // the team model pin BEATS the user's global model (verified on the real binary):
+    expect(cfg.model).toBe(AMICODE_MODEL)
+    // …while non-conflicting user keys still survive the deep-merge:
     expect(cfg.permission.doom_loop).toBe('deny')                  // user permission key preserved (#22)
   })
 })