diff --git a/src/client.test.ts b/src/client.test.ts
index 1c3c819..6685d3c 100644
--- a/src/client.test.ts
+++ b/src/client.test.ts
@@ -3,7 +3,8 @@
  */
 
 import { afterEach, beforeEach, describe, expect, it } from "bun:test"
-import { loadConfig, type PluginConfig, parseBooleanEnv } from "./client"
+import manifest from "../package.json" with { type: "json" }
+import { BraintrustClient, loadConfig, type PluginConfig, parseBooleanEnv } from "./client"
 
 describe("parseBooleanEnv", () => {
   it("returns false for undefined", () => {
@@ -294,3 +295,42 @@ describe("loadConfig", () => {
     })
   })
 })
+
+describe("BraintrustClient span origin", () => {
+  const originalFetch = globalThis.fetch
+
+  afterEach(() => {
+    globalThis.fetch = originalFetch
+  })
+
+  it("uses the package.json version for span origin provenance", async () => {
+    let payload: { events?: Array<{ context?: { span_origin?: { version?: string } } }> } = {}
+    globalThis.fetch = (async (_url: string | URL | Request, init?: RequestInit) => {
+      payload = JSON.parse(String(init?.body))
+      return new Response(JSON.stringify({ row_ids: ["row-id"] }), { status: 200 })
+    }) as typeof fetch
+
+    const client = new BraintrustClient({
+      apiKey: "key",
+      apiUrl: "https://api.example.com",
+      appUrl: "https://app.example.com",
+      projectName: "project",
+      tracingEnabled: true,
+      enableTools: true,
+      debug: false,
+    })
+    Object.assign(client, {
+      initPromise: Promise.resolve(),
+      projectId: "project-id",
+      resolvedApiUrl: "https://api.example.com",
+    })
+
+    await client.insertSpan({
+      id: "span-id",
+      span_id: "span-id",
+      root_span_id: "span-id",
+    })
+
+    expect(payload.events?.[0]?.context?.span_origin?.version).toBe(manifest.version)
+  })
+})
diff --git a/src/client.ts b/src/client.ts
index afc8008..eb440d2 100644
--- a/src/client.ts
+++ b/src/client.ts
@@ -2,6 +2,8 @@
  * Braintrust API client for the OpenCode plugin
  */
 
+import { PLUGIN_VERSION } from "./version"
+
 export interface BraintrustConfig {
   apiKey: string
   apiUrl?: string
@@ -60,6 +62,7 @@ export interface SpanData {
     caller_functionname?: string
     caller_filename?: string
     caller_lineno?: number
+    span_origin?: Record<string, unknown>
   }
   span_attributes?: {
     name?: string
@@ -68,6 +71,62 @@ export interface SpanData {
   _is_merge?: boolean // When true, merge with existing span by id instead of creating new row
 }
 
+function detectEnvironment(): { type?: string; name?: string } | undefined {
+  if (process.env.BRAINTRUST_ENVIRONMENT_TYPE || process.env.BRAINTRUST_ENVIRONMENT_NAME) {
+    return {
+      ...(process.env.BRAINTRUST_ENVIRONMENT_TYPE
+        ? { type: process.env.BRAINTRUST_ENVIRONMENT_TYPE }
+        : {}),
+      ...(process.env.BRAINTRUST_ENVIRONMENT_NAME
+        ? { name: process.env.BRAINTRUST_ENVIRONMENT_NAME }
+        : {}),
+    }
+  }
+  if (process.env.GITHUB_ACTIONS) return { type: "ci", name: "github_actions" }
+  if (process.env.GITLAB_CI) return { type: "ci", name: "gitlab_ci" }
+  if (process.env.CIRCLECI) return { type: "ci", name: "circleci" }
+  if (process.env.BUILDKITE) return { type: "ci", name: "buildkite" }
+  if (process.env.CI) return { type: "ci", name: "ci" }
+  if (process.env.VERCEL) return { type: "server", name: "vercel" }
+  if (process.env.NETLIFY) return { type: "server", name: "netlify" }
+  if (
+    process.env.ECS_CONTAINER_METADATA_URI ||
+    process.env.ECS_CONTAINER_METADATA_URI_V4 ||
+    process.env.AWS_EXECUTION_ENV?.startsWith("AWS_ECS_")
+  ) {
+    return { type: "server", name: "ecs" }
+  }
+  if (
+    process.env.AWS_LAMBDA_FUNCTION_NAME ||
+    process.env.AWS_EXECUTION_ENV?.startsWith("AWS_Lambda_")
+  ) {
+    return { type: "server", name: "aws_lambda" }
+  }
+  if (process.env.NODE_ENV === "production" || process.env.NODE_ENV === "staging") {
+    return { type: "server", name: process.env.NODE_ENV }
+  }
+  if (process.env.NODE_ENV === "development" || process.env.NODE_ENV === "local") {
+    return { type: "local", name: process.env.NODE_ENV }
+  }
+  return undefined
+}
+
+function withSpanOrigin(span: SpanData): SpanData {
+  const environment = detectEnvironment()
+  return {
+    ...span,
+    context: {
+      ...(span.context ?? {}),
+      span_origin: {
+        name: "braintrust.plugin.opencode",
+        version: PLUGIN_VERSION,
+        instrumentation: { name: "opencode-tracing" },
+        ...(environment ? { environment } : {}),
+      },
+    },
+  }
+}
+
 interface LoginResponse {
   org_info: Array<{
     name: string
@@ -345,7 +404,8 @@ export class BraintrustClient {
     }
 
     try {
-      const payload = { events: [span] }
+      const enrichedSpan = withSpanOrigin(span)
+      const payload = { events: [enrichedSpan] }
       debugLog?.("insertSpan: sending", {
         spanId: span.span_id,
         isMerge: span._is_merge,
diff --git a/src/version.ts b/src/version.ts
new file mode 100644
index 0000000..b01a794
--- /dev/null
+++ b/src/version.ts
@@ -0,0 +1,5 @@
+// Read the package version at build/bundle time so package.json remains the
+// single source of truth for span origin provenance.
+import manifest from "../package.json" with { type: "json" }
+
+export const PLUGIN_VERSION: string = manifest.version