diff --git a/docker/Dockerfile b/docker/Dockerfile
index efb3b1e..18964f5 100644
--- a/docker/Dockerfile
+++ b/docker/Dockerfile
@@ -13,6 +13,8 @@
 #
 # Runtime environment:
 #   OPENAI_API_KEY        required for model calls (checked at call time)
+#   AGENT_MODEL, GUARDRAIL_MODEL, COMPACTOR_MODEL
+#                         optional "provider:model" overrides of the models
 #   SANDBOX_PROVIDER      "local" (default) or "modal"
 #   MODAL_TOKEN_ID/SECRET credentials for the modal sandbox provider
 #   RESTATE_ADMIN_URL     admin API for dynamic tool discovery (default
diff --git a/docs/configuration.md b/docs/configuration.md
index 231ac23..888819b 100644
--- a/docs/configuration.md
+++ b/docs/configuration.md
@@ -18,6 +18,7 @@ The agent service reads these environment variables:
 | `MCP_SERVERS_JSON` | MCP servers the agents may use; see below |
 | `SANDBOX_PROVIDER` | `local` (default) or `modal`, which also needs `MODAL_TOKEN_ID` and `MODAL_TOKEN_SECRET` |
 | `MODAL_APP_NAME`, `MODAL_SANDBOX_NAMESPACE`, `MODAL_SANDBOX_IMAGE`, `MODAL_SANDBOX_TIMEOUT_MS` | Optional Modal settings; see [sandboxes](sandboxes.md) |
+| `AGENT_MODEL`, `GUARDRAIL_MODEL`, `COMPACTOR_MODEL` | Override the agent, guardrail and compactor models, as `provider:model`; see [models](#models) |
 | `AGENT_MODEL_MAX_OUTPUT_TOKENS` | Output budget per model call, 1024–64000 (default 32000) |
 | `RESTATE_ADMIN_URL`, `RESTATE_ADMIN_TOKEN` | Admin API used to discover dynamic tools |
 
@@ -44,6 +45,16 @@ models: {
 },
 ```
 
+Each can also be set from the environment without editing the code:
+`AGENT_MODEL`, `GUARDRAIL_MODEL` and `COMPACTOR_MODEL` override the agent,
+guardrail and compactor models, and an unset or empty variable keeps the
+default from `agent-config.ts`. The service reads them at startup.
+
+```sh
+export AGENT_MODEL=anthropic:claude-sonnet-5
+export COMPACTOR_MODEL=google:gemini-3.8-flash
+```
+
 Only the providers in use need an API key. Every call asks for low reasoning,
 and each provider maps that to its own setting. When the agent model changes,
 set `context.windowTokens` to its context window.
diff --git a/packages/libs/core/src/agent-config.ts b/packages/libs/core/src/agent-config.ts
index 5db0630..80670f4 100644
--- a/packages/libs/core/src/agent-config.ts
+++ b/packages/libs/core/src/agent-config.ts
@@ -38,6 +38,11 @@ import {
 import {getWeatherTool} from "./tools/weather.js";
 import {webSearchTool} from "./tools/web-search.js";
 
+/** An environment variable's value, or the default when it is unset or blank. */
+function fromEnv(name: string, fallback: string): string {
+  return process.env[name]?.trim() || fallback;
+}
+
 export const agentConfig = {
   /**
    * The models, as "provider:model", where the provider is openai,
@@ -45,17 +50,21 @@ export const agentConfig = {
    * model/provider.ts and docs/configuration.md). Each provider needs its API
    * key in the service's environment. The three may use different providers.
    *
+   * AGENT_MODEL, GUARDRAIL_MODEL and COMPACTOR_MODEL override them from the
+   * environment; they are read once, at module load, so a change needs a
+   * restart.
+   *
    * A turn keeps one model: its working messages carry that provider's
    * reasoning and tool-call data. Running turns finish on the version they
    * started on, so a change here applies to new turns.
    */
   models: {
     /** Runs the agent's turns. */
-    agent: "openai:gpt-5.6-luna",
+    agent: fromEnv("AGENT_MODEL", "openai:gpt-5.6-luna"),
     /** Evaluates and reviews proposed actions against the guardrails. */
-    guardrail: "openai:gpt-5.6-terra",
+    guardrail: fromEnv("GUARDRAIL_MODEL", "openai:gpt-5.6-terra"),
     /** Summarizes older conversation for later turns. */
-    compactor: "openai:gpt-5.6-terra",
+    compactor: fromEnv("COMPACTOR_MODEL", "openai:gpt-5.6-terra"),
   },
 
   /**
diff --git a/packages/libs/core/test/model-env.test.mjs b/packages/libs/core/test/model-env.test.mjs
new file mode 100644
index 0000000..0a2b1e5
--- /dev/null
+++ b/packages/libs/core/test/model-env.test.mjs
@@ -0,0 +1,46 @@
+import assert from "node:assert/strict";
+import {execFile} from "node:child_process";
+import {test} from "node:test";
+import {promisify} from "node:util";
+
+// agentConfig reads the model variables once, at module load, so each case
+// loads it in a fresh process with its own environment.
+const probe = `
+  const {agentConfig} = await import("./src/agent-config.ts");
+  console.log(JSON.stringify(agentConfig.models));
+`;
+
+async function modelsWith(env) {
+  const base = {...process.env};
+  for (const name of ["AGENT_MODEL", "GUARDRAIL_MODEL", "COMPACTOR_MODEL"])
+    delete base[name];
+  const {stdout} = await promisify(execFile)(
+    process.execPath,
+    ["--import", "tsx", "--input-type=module", "-e", probe],
+    {cwd: new URL("..", import.meta.url), env: {...base, ...env}},
+  );
+  return JSON.parse(stdout.trim().split("\n").at(-1));
+}
+
+test("the model variables override the configured models", async () => {
+  const defaults = await modelsWith({});
+  assert.deepEqual(
+    await modelsWith({
+      AGENT_MODEL: "anthropic:claude-sonnet-5",
+      GUARDRAIL_MODEL: " xai:grok-5 ",
+      COMPACTOR_MODEL: "google:gemini-3.8-flash",
+    }),
+    {
+      agent: "anthropic:claude-sonnet-5",
+      guardrail: "xai:grok-5",
+      compactor: "google:gemini-3.8-flash",
+    },
+  );
+  assert.deepEqual(
+    await modelsWith({
+      AGENT_MODEL: "deepseek:deepseek-chat",
+      COMPACTOR_MODEL: "",
+    }),
+    {...defaults, agent: "deepseek:deepseek-chat"},
+  );
+});