diff --git a/opencode-plugin/src/index.ts b/opencode-plugin/src/index.ts
index c5335e1..d762e89 100644
--- a/opencode-plugin/src/index.ts
+++ b/opencode-plugin/src/index.ts
@@ -275,8 +275,9 @@ const MnemosynePlugin: Plugin = async (ctx: PluginInput): Promise<Hooks> => {
 
       // Only set if not already overridden by user
       if (!inputConfig.provider.anthropic.options.baseURL) {
-        inputConfig.provider.anthropic.options.baseURL = gateway.url;
-        log.info(`Routing Anthropic through gateway at ${gateway.url}`);
+        // Anthropic SDK appends /messages to baseURL, so we need /v1 suffix
+        inputConfig.provider.anthropic.options.baseURL = `${gateway.url}/v1`;
+        log.info(`Routing Anthropic through gateway at ${gateway.url}/v1`);
       } else {
         log.debug(
           `baseURL already set to ${inputConfig.provider.anthropic.options.baseURL}, not overriding`