diff --git a/core/config/defaults.go b/core/config/defaults.go
index 18625fab3..bb993d075 100644
--- a/core/config/defaults.go
+++ b/core/config/defaults.go
@@ -12,14 +12,12 @@ package config
 // these; config never imports backend.
 const (
 	// DefaultContextSize is the fallback context window when none is configured
-	// or estimable from the model.
+	// or estimable from the model. It is also the fallback for a GGUF whose
+	// metadata yields no usable estimate or that the parser cannot read at all
+	// (e.g. a quant type it does not know, such as NVFP4): a model-agnostic
+	// safe default beats a tiny, surprising window that truncates real prompts.
 	DefaultContextSize = 4096
 
-	// GGUFFallbackContextSize is the context window for a GGUF model whose
-	// metadata yields no usable estimate (see guessGGUFFromFile). Deliberately
-	// smaller than DefaultContextSize to stay conservative on memory there.
-	GGUFFallbackContextSize = 1024
-
 	// DefaultNGPULayers means "offload all layers"; the backend (fit_params)
 	// clamps to what actually fits in device memory.
 	DefaultNGPULayers = 99999999
diff --git a/core/config/gguf.go b/core/config/gguf.go
index 16e43c914..177e68749 100644
--- a/core/config/gguf.go
+++ b/core/config/gguf.go
@@ -33,7 +33,7 @@ func guessGGUFFromFile(cfg *ModelConfig, f *gguf.GGUFFile, defaultCtx int) {
 			cSize := int(ctxSize)
 			cfg.ContextSize = &cSize
 		} else {
-			defaultCtx = GGUFFallbackContextSize
+			defaultCtx = DefaultContextSize
 			cfg.ContextSize = &defaultCtx
 		}
 	}
diff --git a/core/config/hooks_llamacpp.go b/core/config/hooks_llamacpp.go
index 09bdbe868..07ccdda7b 100644
--- a/core/config/hooks_llamacpp.go
+++ b/core/config/hooks_llamacpp.go
@@ -34,7 +34,7 @@ func llamaCppDefaults(cfg *ModelConfig, modelPath string) {
 	// Default context size if not set, regardless of whether GGUF parsing succeeds
 	defer func() {
 		if cfg.ContextSize == nil {
-			ctx := GGUFFallbackContextSize
+			ctx := DefaultContextSize
 			cfg.ContextSize = &ctx
 		}
 	}()
diff --git a/core/config/hooks_test.go b/core/config/hooks_test.go
index 6e18ad7cc..a1b30b8d9 100644
--- a/core/config/hooks_test.go
+++ b/core/config/hooks_test.go
@@ -248,7 +248,11 @@ var _ = Describe("Backend hooks and parser defaults", func() {
 			}
 			cfg.SetDefaults(ModelPath(dir))
 
+			// An unreadable/unparseable GGUF (e.g. a quant type the parser does
+			// not know, such as NVFP4) yields no estimate, so the hook must fall
+			// back to DefaultContextSize rather than a tiny, surprising value.
 			Expect(cfg.ContextSize).NotTo(BeNil())
+			Expect(*cfg.ContextSize).To(Equal(DefaultContextSize))
 		})
 	})
 
diff --git a/gallery/index.yaml b/gallery/index.yaml
index cc975a83a..f39993333 100644
--- a/gallery/index.yaml
+++ b/gallery/index.yaml
@@ -579,6 +579,10 @@
   icon: https://qianwen-res.oss-cn-beijing.aliyuncs.com/Qwen3.6/Figures/qwen3.6_35b_a3b_score.png
   overrides:
     backend: llama-cpp
+    # NVFP4 GGUFs use a quant type the GGUF metadata parser cannot read, so
+    # context size cannot be auto-derived; set it explicitly (the model trains
+    # to 262144, 32768 is a safe default operators can raise).
+    context_size: 32768
     function:
       automatic_tool_parsing_fallback: true
       grammar:
@@ -611,6 +615,9 @@
     - gguf
   overrides:
     backend: llama-cpp
+    # NVFP4 GGUFs use a quant type the GGUF metadata parser cannot read, so
+    # context size cannot be auto-derived; set it explicitly.
+    context_size: 32768
     function:
       automatic_tool_parsing_fallback: true
       grammar:
@@ -638,6 +645,9 @@
   icon: https://cdn-uploads.huggingface.co/production/uploads/66309bd090589b7c65950665/sGQKmrMc6L6guMoaB5_Y2.png
   overrides:
     backend: llama-cpp
+    # NVFP4 GGUFs use a quant type the GGUF metadata parser cannot read, so
+    # context size cannot be auto-derived; set it explicitly.
+    context_size: 32768
     function:
       automatic_tool_parsing_fallback: true
       grammar:
@@ -688,6 +698,10 @@
   icon: https://qianwen-res.oss-cn-beijing.aliyuncs.com/Qwen3.6/Figures/qwen3.6_27b_score.png
   overrides:
     backend: llama-cpp
+    # NVFP4 GGUFs use a quant type the GGUF metadata parser cannot read, so
+    # context size cannot be auto-derived; set it explicitly (the model trains
+    # to 262144, 32768 is a safe default operators can raise).
+    context_size: 32768
     function:
       automatic_tool_parsing_fallback: true
       grammar: