From e9fd8dcab45d6cd147874e32565923bdfd0efbdb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Johannes=20G=C3=A4=C3=9Fler?= <johannesg@5d6.de>
Date: Sat, 24 Jan 2026 22:13:08 +0100
Subject: [PATCH] llama-fit-params: keep explicit --ctx-size 0 (#19070)

---
 common/arg.cpp                  | 4 ++++
 include/llama.h                 | 1 +
 src/llama.cpp                   | 8 ++++++--
 tools/fit-params/fit-params.cpp | 2 +-
 4 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/common/arg.cpp b/common/arg.cpp
index 163c9b71b0..98477e8117 100644
--- a/common/arg.cpp
+++ b/common/arg.cpp
@@ -1231,6 +1231,10 @@ common_params_context common_params_parser_init(common_params & params, llama_ex
         string_format("size of the prompt context (default: %d, 0 = loaded from model)", params.n_ctx),
         [](common_params & params, int value) {
             params.n_ctx = value;
+            if (value == 0) {
+                // disable context reduction in llama_params_fit if the user explicitly requests the full context size:
+                params.fit_params_min_ctx = UINT32_MAX;
+            }
         }
     ).set_env("LLAMA_ARG_CTX_SIZE"));
     add_opt(common_arg(
diff --git a/include/llama.h b/include/llama.h
index 280745713e..1507107f1a 100644
--- a/include/llama.h
+++ b/include/llama.h
@@ -489,6 +489,7 @@ extern "C" {
     //   - returns true if the parameters could be successfully modified to fit device memory
     //   - this function is NOT thread safe because it modifies the global llama logger state
     //   - only parameters that have the same value as in llama_default_model_params are modified
+    //     with the exception of the context size which is modified if and only if equal to 0
     LLAMA_API enum llama_params_fit_status llama_params_fit(
                                    const char   * path_model,
                     struct llama_model_params   * mparams,
diff --git a/src/llama.cpp b/src/llama.cpp
index f1096d960e..11b75fcff9 100644
--- a/src/llama.cpp
+++ b/src/llama.cpp
@@ -311,8 +311,12 @@ static void llama_params_fit_impl(
                             __func__, hp_nct, cparams->n_ctx, memory_reduction/MiB);
                     }
                 } else {
-                    LLAMA_LOG_INFO("%s: default model context size is %" PRIu32 " which is <= the min. context size of %" PRIu32 " -> no change\n",
-                        __func__, hp_nct, n_ctx_min);
+                    if (n_ctx_min == UINT32_MAX) {
+                        LLAMA_LOG_INFO("%s: user has requested full context size of %" PRIu32 " -> no change\n", __func__, hp_nct);
+                    } else {
+                        LLAMA_LOG_INFO("%s: default model context size is %" PRIu32 " which is <= the min. context size of %" PRIu32 " -> no change\n",
+                            __func__, hp_nct, n_ctx_min);
+                    }
                 }
             } else {
                 LLAMA_LOG_INFO("%s: context size set by user to %" PRIu32 " -> no change\n", __func__, cparams->n_ctx);
diff --git a/tools/fit-params/fit-params.cpp b/tools/fit-params/fit-params.cpp
index f9d9cb34c7..0176be06e7 100644
--- a/tools/fit-params/fit-params.cpp
+++ b/tools/fit-params/fit-params.cpp
@@ -36,7 +36,7 @@ int main(int argc, char ** argv) {
 
     LOG_INF("%s: printing fitted CLI arguments to stdout...\n", __func__);
     common_log_flush(common_log_main());
-    printf("-c %" PRIu32 " -ngl %" PRIu32, cparams.n_ctx, mparams.n_gpu_layers);
+    printf("-c %" PRIu32 " -ngl %" PRIi32, cparams.n_ctx, mparams.n_gpu_layers);
 
     size_t nd = llama_max_devices();
     while (nd > 1 && mparams.tensor_split[nd - 1] == 0.0f) {