diff --git a/open-sse/config/providers/registry/cline/index.ts b/open-sse/config/providers/registry/cline/index.ts
index d1467fdd9f..4913465d19 100644
--- a/open-sse/config/providers/registry/cline/index.ts
+++ b/open-sse/config/providers/registry/cline/index.ts
@@ -5,6 +5,11 @@ export const clineProvider: RegistryEntry = {
   alias: "cl",
   format: "openai",
   executor: "openai",
+  // Cline's API only implements streaming (streamText). A non-streaming request
+  // returns "generateText is not implemented" / an empty body, so force upstream
+  // streaming and let chatCore convert the SSE back to JSON for stream:false
+  // clients (e.g. the model-test button, non-streaming API callers).
+  forceStream: true,
   baseUrl: "https://api.cline.bot/api/v1/chat/completions",
   authType: "oauth",
   authHeader: "Authorization",
diff --git a/open-sse/config/providers/registry/clinepass/index.ts b/open-sse/config/providers/registry/clinepass/index.ts
index 3ea7dbcb3a..e6d3697a03 100644
--- a/open-sse/config/providers/registry/clinepass/index.ts
+++ b/open-sse/config/providers/registry/clinepass/index.ts
@@ -9,6 +9,11 @@ export const clinepassProvider: RegistryEntry = {
   alias: "clinepass",
   format: "openai",
   executor: "default",
+  // ClinePass shares Cline's streaming-only API — a non-streaming request returns
+  // "generateText is not implemented" / an empty body. Force upstream streaming;
+  // chatCore accumulates the SSE and converts it back to JSON for stream:false
+  // clients. (Same as the sibling `cline` provider.)
+  forceStream: true,
   baseUrl: "https://api.cline.bot/api/v1/chat/completions",
   authType: "apikey",
   authHeader: "bearer",
diff --git a/open-sse/handlers/chatCore.ts b/open-sse/handlers/chatCore.ts
index e6f7cb7391..54657d6737 100644
--- a/open-sse/handlers/chatCore.ts
+++ b/open-sse/handlers/chatCore.ts
@@ -873,9 +873,16 @@ export async function handleChatCore({
   // sourceFormat="claude" applies the Anthropic Messages spec default (stream=false
   // when body omits stream), preventing STREAM_EARLY_EOF on /v1/messages when
   // clients send Accept: */* without an explicit stream flag.
-  // providerRequiresStreaming: providers with forceStream:true reject stream:false
-  // upstream (HTTP 400); keep streaming so OmniRoute can convert the stream to JSON
-  // for the client via handleForcedSSEToJson. (#2081)
+  // providerRequiresStreaming: providers with forceStream:true (cline/clinepass)
+  // only implement upstream streaming — a non-streaming request returns
+  // "generateText is not implemented" / an empty body. This flag forces the
+  // UPSTREAM request to stream (see `upstreamStream` below), but it MUST NOT
+  // force the client-facing `stream` flag: a stream:false client (e.g. the
+  // model-test button, plain JSON API callers) still expects a JSON response.
+  // The client-side `if (!stream)` branch drains the forced upstream SSE and
+  // converts it back to JSON via readNonStreamingResponseBody. Passing this
+  // flag into resolveStreamFlag would force `stream=true` and skip that
+  // conversion, yielding STREAM_EARLY_EOF for JSON callers. (#2081, #6126)
   const providerRequiresStreaming = REGISTRY[provider]?.forceStream === true;
   const stream =
     nativeCodexPassthrough && isCompactResponsesEndpoint(endpointPath)
@@ -883,7 +890,6 @@ export async function handleChatCore({
       : resolveStreamFlag(body?.stream, acceptHeader, sourceFormat, {
           userAgent: streamUserAgent,
           streamDefaultMode: apiKeyInfo?.streamDefaultMode,
-          providerRequiresStreaming,
         });
 
   // `settings` is already consolidated once near the top of handleChatCore
@@ -1588,7 +1594,13 @@ export async function handleChatCore({
     headers: clientRawRequest?.headers,
     userAgent,
   });
-  const upstreamStream = stream || isClaudeCodeCompatible;
+  // `forceStream` providers (e.g. Cline / ClinePass) only implement upstream
+  // streaming — a non-streaming request returns "generateText is not implemented"
+  // / an empty body. Force the upstream request to stream even when the client
+  // wants JSON; the non-streaming branch below accumulates the SSE and converts
+  // it back to JSON (same mechanism already used for Claude-Code-compatible
+  // providers via isClaudeCodeCompatible).
+  const upstreamStream = stream || isClaudeCodeCompatible || providerRequiresStreaming;
   let ccSessionId: string | null = null;
   const stripTypes = getStripTypesForProviderModel(provider || "", model || "");
 
diff --git a/tests/unit/cline-force-stream.test.ts b/tests/unit/cline-force-stream.test.ts
new file mode 100644
index 0000000000..2c8ea5caaf
--- /dev/null
+++ b/tests/unit/cline-force-stream.test.ts
@@ -0,0 +1,43 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+
+import { REGISTRY } from "@omniroute/open-sse/config/providers/index.ts";
+import { resolveStreamFlag } from "@omniroute/open-sse/utils/aiSdkCompat.ts";
+
+// Cline / ClinePass only implement upstream streaming — a non-streaming request
+// returns "generateText is not implemented" / an empty body. They carry
+// `forceStream: true` so chatCore forces the UPSTREAM request to stream
+// (`upstreamStream = stream || isClaudeCodeCompatible || providerRequiresStreaming`)
+// even when the client wants JSON. The client-facing `stream` flag stays as the
+// client sent it, so the `if (!stream)` branch drains the forced upstream SSE and
+// converts it back to JSON via readNonStreamingResponseBody. Regression guard for
+// the "cline model test → generateText is not implemented / STREAM_EARLY_EOF" bug
+// (live-verified on the VPS: stream:true works, stream:false failed). (#6126)
+
+test("cline provider is flagged forceStream (streaming-only upstream)", () => {
+  assert.equal(REGISTRY.cline?.forceStream, true);
+});
+
+test("clinepass provider is flagged forceStream (streaming-only upstream)", () => {
+  assert.equal(REGISTRY.clinepass?.forceStream, true);
+});
+
+test("upstreamStream is forced true for a forceStream provider even when the client sent stream:false", () => {
+  // Mirror the chatCore wiring: providerRequiresStreaming derives from the
+  // registry flag, and upstreamStream ORs it in so the upstream always streams.
+  const providerRequiresStreaming = REGISTRY.cline?.forceStream === true;
+  const isClaudeCodeCompatible = false;
+  const clientStream = false; // client asked for JSON
+  const upstreamStream = clientStream || isClaudeCodeCompatible || providerRequiresStreaming;
+  assert.equal(upstreamStream, true);
+});
+
+test("client-facing stream stays false for a stream:false JSON caller (so SSE→JSON conversion runs)", () => {
+  // chatCore MUST NOT pass providerRequiresStreaming into resolveStreamFlag:
+  // a stream:false client keeps stream=false so the `if (!stream)` branch drains
+  // the forced upstream SSE and returns JSON. Forcing stream=true here would skip
+  // that conversion and yield STREAM_EARLY_EOF for JSON callers.
+  assert.equal(resolveStreamFlag(false, "application/json", "openai"), false);
+  // A stream:true client still streams end-to-end.
+  assert.equal(resolveStreamFlag(true, "application/json", "openai"), true);
+});