diff --git a/lib/compress/zstd_compress.c b/lib/compress/zstd_compress.c
index 860bc2888..b2f025dc6 100644
--- a/lib/compress/zstd_compress.c
+++ b/lib/compress/zstd_compress.c
@@ -1367,6 +1367,33 @@ typedef char ZSTD_rust_compress_using_cdict_state_layout[
                 == 3 * sizeof(void*)
          && sizeof(ZSTD_rust_compressUsingCDictState) == 4 * sizeof(void*))
         ? 1 : -1];
+typedef void (*ZSTD_rust_compressBeginUsingDictInitParams_f)(
+        void* cctxParams, const ZSTD_parameters* params, int compressionLevel);
+typedef size_t (*ZSTD_rust_compressBeginUsingDictBegin_f)(
+        void* context, const void* dict, size_t dictSize,
+        const void* cctxParams, U64 pledgedSrcSize);
+typedef struct {
+    void* cctx;
+    void* cctxParams;
+    const U32* exclusionMask;
+    ZSTD_rust_compressBeginUsingDictInitParams_f initParams;
+    ZSTD_rust_compressBeginUsingDictBegin_f begin;
+} ZSTD_rust_compressBeginUsingDictState;
+size_t ZSTD_rust_compressBeginUsingDict(
+        const ZSTD_rust_compressBeginUsingDictState* state,
+        const void* dict, size_t dictSize, int compressionLevel);
+typedef char ZSTD_rust_compress_begin_using_dict_state_layout[
+        (offsetof(ZSTD_rust_compressBeginUsingDictState, cctx) == 0
+         && offsetof(ZSTD_rust_compressBeginUsingDictState, cctxParams)
+                == sizeof(void*)
+         && offsetof(ZSTD_rust_compressBeginUsingDictState, exclusionMask)
+                == 2 * sizeof(void*)
+         && offsetof(ZSTD_rust_compressBeginUsingDictState, initParams)
+                == 3 * sizeof(void*)
+         && offsetof(ZSTD_rust_compressBeginUsingDictState, begin)
+                == 4 * sizeof(void*)
+         && sizeof(ZSTD_rust_compressBeginUsingDictState) == 5 * sizeof(void*))
+        ? 1 : -1];
 typedef struct {
     const ZSTD_compressionParameters* cParams;
     const unsigned* dictID;
@@ -4796,6 +4823,24 @@ static size_t ZSTD_compressBegin_internal(ZSTD_CCtx* cctx,
     return ZSTD_rust_compressBegin(&state);
 }
 
+static void ZSTD_rust_compressBeginUsingDict_initParams(
+        void* cctxParams, const ZSTD_parameters* params, int compressionLevel)
+{
+    ZSTD_CCtxParams_init_internal(
+            (ZSTD_CCtx_params*)cctxParams, params, compressionLevel);
+}
+
+static size_t ZSTD_rust_compressBeginUsingDict_begin(
+        void* context, const void* dict, size_t dictSize,
+        const void* cctxParams, U64 pledgedSrcSize)
+{
+    return ZSTD_compressBegin_internal(
+            (ZSTD_CCtx*)context, dict, dictSize,
+            ZSTD_dct_auto, ZSTD_dtlm_fast, NULL,
+            (const ZSTD_CCtx_params*)cctxParams,
+            pledgedSrcSize, ZSTDb_not_buffered);
+}
+
 size_t ZSTD_compressBegin_advanced_internal(ZSTD_CCtx* cctx,
                                     const void* dict, size_t dictSize,
                                     ZSTD_dictContentType_e dictContentType,
@@ -4831,13 +4876,17 @@ size_t ZSTD_compressBegin_advanced(ZSTD_CCtx* cctx,
 static size_t
 ZSTD_compressBegin_usingDict_deprecated(ZSTD_CCtx* cctx, const void* dict, size_t dictSize, int compressionLevel)
 {
+    ZSTD_rust_compressBeginUsingDictState state;
     ZSTD_CCtx_params cctxParams;
-    {   ZSTD_parameters const params = ZSTD_getParams_internal(compressionLevel, ZSTD_CONTENTSIZE_UNKNOWN, dictSize, ZSTD_cpm_noAttachDict);
-        ZSTD_CCtxParams_init_internal(&cctxParams, &params, (compressionLevel == 0) ? ZSTD_CLEVEL_DEFAULT : compressionLevel);
-    }
+    U32 const exclusionMask = ZSTD_getCParamsExclusionMask();
     DEBUGLOG(4, "ZSTD_compressBegin_usingDict (dictSize=%u)", (unsigned)dictSize);
-    return ZSTD_compressBegin_internal(cctx, dict, dictSize, ZSTD_dct_auto, ZSTD_dtlm_fast, NULL,
-                                       &cctxParams, ZSTD_CONTENTSIZE_UNKNOWN, ZSTDb_not_buffered);
+    state.cctx = cctx;
+    state.cctxParams = &cctxParams;
+    state.exclusionMask = &exclusionMask;
+    state.initParams = ZSTD_rust_compressBeginUsingDict_initParams;
+    state.begin = ZSTD_rust_compressBeginUsingDict_begin;
+    return ZSTD_rust_compressBeginUsingDict(
+            &state, dict, dictSize, compressionLevel);
 }
 
 size_t
diff --git a/rust/src/zstd_compress_dictionary.rs b/rust/src/zstd_compress_dictionary.rs
index e27867ada..fca4d6e21 100644
--- a/rust/src/zstd_compress_dictionary.rs
+++ b/rust/src/zstd_compress_dictionary.rs
@@ -16,8 +16,10 @@ use crate::errors::{ERR_isError, ZstdErrorCode, ERROR};
 use crate::fse_compress::FSE_buildCTable_wksp;
 use crate::huf_compress::HUF_readCTable;
 use crate::zstd_compress_params::{
-    ZSTD_compressionParameters, ZSTD_frameParameters, ZSTD_parameters, ZSTD_rust_params_getCParams,
-    ZSTD_rust_params_shouldAttachDict, ZSTD_CONTENTSIZE_UNKNOWN,
+    ZSTD_compressionParameters, ZSTD_frameParameters, ZSTD_parameters,
+    ZSTD_rust_params_defaultCLevel, ZSTD_rust_params_getCParams,
+    ZSTD_rust_params_getParamsInternal, ZSTD_rust_params_shouldAttachDict,
+    ZSTD_CONTENTSIZE_UNKNOWN, ZSTD_RUST_CPM_NO_ATTACH_DICT,
 };
 use crate::zstd_compress_params_api::ZSTD_CCtx_params;
 use crate::zstd_compress_stats::{
@@ -297,6 +299,76 @@ pub unsafe extern "C" fn ZSTD_rust_compressUsingCDict(
     unsafe { (state.end)(state.callback_context, dst, dst_capacity, src, src_size) }
 }
 
+type CompressBeginUsingDictBeginFn =
+    unsafe extern "C" fn(*mut c_void, *const c_void, usize, *const c_void, u64) -> usize;
+
+/// Explicit projection for the public `ZSTD_compressBegin_usingDict` family.
+///
+/// Rust owns unknown-source parameter selection and default-level
+/// normalization. C retains private `ZSTD_CCtx_params` initialization and the
+/// final `ZSTD_compressBegin_internal` call behind callbacks.
+#[repr(C)]
+pub struct ZSTD_rust_compressBeginUsingDictState {
+    cctx: *mut c_void,
+    cctx_params: *mut ZSTD_CCtx_params,
+    exclusion_mask: *const c_uint,
+    init_params: CompressBeginUsingCDictInitParamsFn,
+    begin: CompressBeginUsingDictBeginFn,
+}
+
+const _: () = {
+    assert!(offset_of!(ZSTD_rust_compressBeginUsingDictState, cctx) == 0);
+    assert!(offset_of!(ZSTD_rust_compressBeginUsingDictState, cctx_params) == size_of::<usize>());
+    assert!(
+        offset_of!(ZSTD_rust_compressBeginUsingDictState, exclusion_mask) == 2 * size_of::<usize>()
+    );
+    assert!(
+        offset_of!(ZSTD_rust_compressBeginUsingDictState, init_params) == 3 * size_of::<usize>()
+    );
+    assert!(offset_of!(ZSTD_rust_compressBeginUsingDictState, begin) == 4 * size_of::<usize>());
+    assert!(size_of::<ZSTD_rust_compressBeginUsingDictState>() == size_of::<[usize; 5]>());
+};
+
+/// Select parameters and start a dictionary-backed frame.
+#[no_mangle]
+pub unsafe extern "C" fn ZSTD_rust_compressBeginUsingDict(
+    state: *const ZSTD_rust_compressBeginUsingDictState,
+    dict: *const c_void,
+    dict_size: usize,
+    compression_level: c_int,
+) -> usize {
+    if state.is_null() {
+        return ERROR(ZstdErrorCode::Generic);
+    }
+    let state = unsafe { &*state };
+    if state.cctx.is_null() || state.cctx_params.is_null() || state.exclusion_mask.is_null() {
+        return ERROR(ZstdErrorCode::Generic);
+    }
+
+    let params = ZSTD_rust_params_getParamsInternal(
+        compression_level,
+        ZSTD_CONTENTSIZE_UNKNOWN,
+        dict_size,
+        ZSTD_RUST_CPM_NO_ATTACH_DICT,
+        unsafe { *state.exclusion_mask },
+    );
+    let init_level = if compression_level == 0 {
+        ZSTD_rust_params_defaultCLevel()
+    } else {
+        compression_level
+    };
+    unsafe {
+        (state.init_params)(state.cctx_params.cast(), &params, init_level);
+        (state.begin)(
+            state.cctx,
+            dict,
+            dict_size,
+            state.cctx_params.cast_const().cast(),
+            ZSTD_CONTENTSIZE_UNKNOWN,
+        )
+    }
+}
+
 type InitCDictAssignContentFn =
     unsafe extern "C" fn(*mut c_void, *const c_void, usize, c_int) -> usize;
 type InitCDictReserveEntropyFn = unsafe extern "C" fn(*mut c_void) -> *mut c_void;
@@ -2482,6 +2554,106 @@ mod tests {
         assert_eq!(probe.events, ["begin"]);
     }
 
+    #[derive(Default)]
+    struct CompressBeginUsingDictProbe {
+        events: Vec<&'static str>,
+        params: ZSTD_parameters,
+        compression_level: c_int,
+        dict: *const c_void,
+        dict_size: usize,
+        cctx_params: *const c_void,
+        pledged_src_size: u64,
+        begin_result: usize,
+    }
+
+    unsafe extern "C" fn compress_begin_using_dict_test_init(
+        context: *mut c_void,
+        params: *const ZSTD_parameters,
+        compression_level: c_int,
+    ) {
+        let probe = unsafe { &mut *context.cast::<CompressBeginUsingDictProbe>() };
+        probe.events.push("init");
+        probe.params = unsafe { *params };
+        probe.compression_level = compression_level;
+    }
+
+    unsafe extern "C" fn compress_begin_using_dict_test_begin(
+        context: *mut c_void,
+        dict: *const c_void,
+        dict_size: usize,
+        cctx_params: *const c_void,
+        pledged_src_size: u64,
+    ) -> usize {
+        let probe = unsafe { &mut *context.cast::<CompressBeginUsingDictProbe>() };
+        probe.events.push("begin");
+        probe.dict = dict;
+        probe.dict_size = dict_size;
+        probe.cctx_params = cctx_params;
+        probe.pledged_src_size = pledged_src_size;
+        probe.begin_result
+    }
+
+    fn compress_begin_using_dict_test_state(
+        probe: &mut CompressBeginUsingDictProbe,
+        exclusion_mask: &c_uint,
+    ) -> ZSTD_rust_compressBeginUsingDictState {
+        ZSTD_rust_compressBeginUsingDictState {
+            cctx: (probe as *mut CompressBeginUsingDictProbe).cast(),
+            cctx_params: (probe as *mut CompressBeginUsingDictProbe).cast(),
+            exclusion_mask,
+            init_params: compress_begin_using_dict_test_init,
+            begin: compress_begin_using_dict_test_begin,
+        }
+    }
+
+    #[test]
+    fn compress_begin_using_dict_selects_unknown_source_params_and_default_level() {
+        let mut probe = CompressBeginUsingDictProbe::default();
+        let exclusion_mask = 0;
+        let state = compress_begin_using_dict_test_state(&mut probe, &exclusion_mask);
+        let dict = [1u8, 2, 3];
+
+        let result = unsafe {
+            ZSTD_rust_compressBeginUsingDict(&state, dict.as_ptr().cast(), dict.len(), 0)
+        };
+
+        assert_eq!(result, 0);
+        assert_eq!(probe.events, ["init", "begin"]);
+        assert_eq!(
+            probe.params,
+            ZSTD_rust_params_getParamsInternal(
+                0,
+                ZSTD_CONTENTSIZE_UNKNOWN,
+                dict.len(),
+                ZSTD_RUST_CPM_NO_ATTACH_DICT,
+                exclusion_mask,
+            )
+        );
+        assert_eq!(probe.compression_level, ZSTD_rust_params_defaultCLevel());
+        assert_eq!(probe.dict, dict.as_ptr().cast());
+        assert_eq!(probe.dict_size, dict.len());
+        assert_eq!(
+            probe.cctx_params,
+            (&probe as *const CompressBeginUsingDictProbe).cast()
+        );
+        assert_eq!(probe.pledged_src_size, ZSTD_CONTENTSIZE_UNKNOWN);
+    }
+
+    #[test]
+    fn compress_begin_using_dict_propagates_begin_errors_after_initialization() {
+        let mut probe = CompressBeginUsingDictProbe {
+            begin_result: ERROR(ZstdErrorCode::StageWrong),
+            ..Default::default()
+        };
+        let exclusion_mask = 0;
+        let state = compress_begin_using_dict_test_state(&mut probe, &exclusion_mask);
+
+        let result = unsafe { ZSTD_rust_compressBeginUsingDict(&state, ptr::null(), 0, 3) };
+
+        assert_eq!(result, probe.begin_result);
+        assert_eq!(probe.events, ["init", "begin"]);
+    }
+
     fn assert_dictionary_corrupted(result: usize) {
         assert!(ERR_isError(result));
         assert_eq!(