diff --git a/core/application/router_factories.go b/core/application/router_factories.go
index dff2d5798..0ef663019 100644
--- a/core/application/router_factories.go
+++ b/core/application/router_factories.go
@@ -13,6 +13,7 @@ import (
 	"github.com/mudler/LocalAI/core/backend"
 	"github.com/mudler/LocalAI/core/config"
 	"github.com/mudler/LocalAI/core/services/routing/corpus"
+	"github.com/mudler/LocalAI/pkg/reasoning"
 	"gopkg.in/yaml.v3"
 )
 
@@ -119,7 +120,14 @@ func (a *Application) EmbedderFingerprint(modelName string) (string, error) {
 	if cfg == nil {
 		return "", fmt.Errorf("embedding model %q not available", modelName)
 	}
-	raw, err := yaml.Marshal(cfg)
+	// Reasoning never changes the embedding space, but a chat request against
+	// this model may persist probed reasoning slots into the shared config
+	// (persistProbedReasoning). Hashing them would move the fingerprint on
+	// such a request and leave every knn router built on this embedder failing
+	// with ErrLiveEmbeddingMismatch until restart.
+	hashed := *cfg
+	hashed.ReasoningConfig = reasoning.Config{}
+	raw, err := yaml.Marshal(&hashed)
 	if err != nil {
 		return "", fmt.Errorf("fingerprint embedding model %q config: %w", modelName, err)
 	}
diff --git a/core/application/router_factories_test.go b/core/application/router_factories_test.go
index 7f50d47c2..6e20332d8 100644
--- a/core/application/router_factories_test.go
+++ b/core/application/router_factories_test.go
@@ -137,6 +137,27 @@ var _ = Describe("router_factories lazy config resolution", func() {
 			Expect(updated).NotTo(Equal(replaced))
 		})
 
+		It("stays stable when a chat request persists probed reasoning slots", func() {
+			// A chat completion sent to an embedding model whose config sets
+			// use_tokenizer_template runs the thinking probe, and
+			// persistProbedReasoning writes the probed reasoning slots back into
+			// the shared config. Reasoning never changes the embedding space, so
+			// the fingerprint must not move — otherwise every knn router built
+			// on this embedder fails with ErrLiveEmbeddingMismatch until restart.
+			writeCfg("emb-probe", "llama-cpp")
+			before, err := app.EmbedderFingerprint("emb-probe")
+			Expect(err).NotTo(HaveOccurred())
+
+			disable, prefill := true, false
+			app.backendLoader.UpdateModelConfig("emb-probe", func(c *config.ModelConfig) {
+				c.ReasoningConfig.DisableReasoning = &disable
+				c.ReasoningConfig.DisableReasoningTagPrefill = &prefill
+			})
+			after, err := app.EmbedderFingerprint("emb-probe")
+			Expect(err).NotTo(HaveOccurred())
+			Expect(after).To(Equal(before))
+		})
+
 		It("rejects an unknown model", func() {
 			_, err := app.EmbedderFingerprint("missing")
 			Expect(err).To(HaveOccurred())