diff --git a/himbaechel/uarch/gowin/constids.inc b/himbaechel/uarch/gowin/constids.inc
index 055c6dc20d..a33dc5791a 100644
--- a/himbaechel/uarch/gowin/constids.inc
+++ b/himbaechel/uarch/gowin/constids.inc
@@ -1313,6 +1313,9 @@ X(LSREN)
 // EMCU
 X(EMCU)
 
+// I3C
+X(I3C_IOBUF)
+
 // MIPI
 X(IL)
 X(OH)
diff --git a/himbaechel/uarch/gowin/gowin.h b/himbaechel/uarch/gowin/gowin.h
index c9a0781b59..b064c3622a 100644
--- a/himbaechel/uarch/gowin/gowin.h
+++ b/himbaechel/uarch/gowin/gowin.h
@@ -36,6 +36,10 @@ inline bool is_diffio(const CellInfo *cell) { return type_is_diffio(cell->type);
 inline bool type_is_mipi(IdString cell_type) { return cell_type.in(id_MIPI_OBUF, id_MIPI_OBUF_A, id_MIPI_IBUF); }
 inline bool is_mipi(const CellInfo *cell) { return type_is_mipi(cell->type); }
 
+// I3C
+inline bool type_is_i3c(IdString cell_type) { return cell_type.in(id_I3C_IOBUF); }
+inline bool is_i3c(const CellInfo *cell) { return type_is_i3c(cell->type); }
+
 // IOLOGIC input and output separately
 
 inline bool type_is_iologico(IdString cell_type)
@@ -106,6 +110,7 @@ NPNR_PACKED_STRUCT(struct Tile_extra_data_POD {
     int32_t class_id;
     int16_t io16_x_off;
     int16_t io16_y_off;
+    int32_t i3c_capable;
 });
 
 NPNR_PACKED_STRUCT(struct Bottom_io_cnd_POD {
diff --git a/himbaechel/uarch/gowin/gowin_arch_gen.py b/himbaechel/uarch/gowin/gowin_arch_gen.py
index 9bd27e0059..3bb7fad596 100644
--- a/himbaechel/uarch/gowin/gowin_arch_gen.py
+++ b/himbaechel/uarch/gowin/gowin_arch_gen.py
@@ -126,6 +126,7 @@ class TileExtraData(BBAStruct):
                          # then we assign them to the same LOGIC class.
     io16_x_off: int = 0  # OSER16/IDES16 offsets to the aux cell
     io16_y_off: int = 0
+    i3c_capable: int = 0 # IO can be used as I3C
 
     def serialise_lists(self, context: str, bba: BBAWriter):
         pass
@@ -133,6 +134,7 @@ def serialise(self, context: str, bba: BBAWriter):
         bba.u32(self.tile_class.index)
         bba.u16(self.io16_x_off)
         bba.u16(self.io16_y_off)
+        bba.u32(self.i3c_capable)
 
 @dataclass
 class BottomIOCnd(BBAStruct):
@@ -582,6 +584,8 @@ def create_extra_funcs(tt: TileType, db: chipdb, x: int, y: int):
                         tt.add_bel_pin(bel, port, wire, PinType.OUTPUT)
                     else:
                         tt.add_bel_pin(bel, port, wire, PinType.INPUT)
+        elif func == 'i3c_capable':
+            tt.extra_data.i3c_capable = 1
         elif func == 'mipi_obuf':
             bel = tt.create_bel('MIPI_OBUF', 'MIPI_OBUF', MIPIOBUF_Z)
         elif func == 'mipi_ibuf':
diff --git a/himbaechel/uarch/gowin/gowin_utils.cc b/himbaechel/uarch/gowin/gowin_utils.cc
index ed3571a689..b7ca7aef7c 100644
--- a/himbaechel/uarch/gowin/gowin_utils.cc
+++ b/himbaechel/uarch/gowin/gowin_utils.cc
@@ -30,6 +30,15 @@ Loc GowinUtils::get_tile_io16_offs(int x, int y)
     return Loc(extra->io16_x_off, extra->io16_y_off, 0);
 }
 
+// oser16/ides16 aux cell offsets
+bool GowinUtils::get_i3c_capable(int x, int y)
+{
+    int tile = tile_by_xy(ctx->chip_info, x, y);
+    const Tile_extra_data_POD *extra =
+            reinterpret_cast<const Tile_extra_data_POD *>(chip_tile_info(ctx->chip_info, tile).extra_data.get());
+    return extra->i3c_capable != 0;
+}
+
 // pin functions: GCLKT_4, SSPI_CS, READY etc
 IdStringList GowinUtils::get_pin_funcs(BelId io_bel)
 {
diff --git a/himbaechel/uarch/gowin/gowin_utils.h b/himbaechel/uarch/gowin/gowin_utils.h
index ff622804f4..40894319c7 100644
--- a/himbaechel/uarch/gowin/gowin_utils.h
+++ b/himbaechel/uarch/gowin/gowin_utils.h
@@ -23,6 +23,7 @@ struct GowinUtils
     // tile
     IdString get_tile_class(int x, int y);
     Loc get_tile_io16_offs(int x, int y);
+    bool get_i3c_capable(int x, int y);
 
     // pin functions: GCLKT_4, SSPI_CS, READY etc
     IdStringList get_pin_funcs(BelId io_bel);
diff --git a/himbaechel/uarch/gowin/pack.cc b/himbaechel/uarch/gowin/pack.cc
index c8b23ef699..b2c67c3017 100644
--- a/himbaechel/uarch/gowin/pack.cc
+++ b/himbaechel/uarch/gowin/pack.cc
@@ -308,6 +308,47 @@ struct GowinPacker
         }
     }
 
+    // ===================================
+    // I3C
+    // ===================================
+    void pack_i3c(void)
+    {
+        log_info("Pack I3C IOs...\n");
+        std::vector<IdString> cells_to_remove;
+
+        for (auto &cell : ctx->cells) {
+            CellInfo &ci = *cell.second;
+            if (!is_i3c(&ci)) {
+                continue;
+            }
+            // check for I3C-capable pin A
+            CellInfo *iob = net_only_drives(ctx, ci.ports.at(id_IO).net, is_iob, id_I);
+            if (iob == nullptr || iob->bel == BelId()) {
+                log_error("I3C %s IO is not connected to the input pin or the pin is not constrained.\n",
+                          ctx->nameOf(&ci));
+            }
+            BelId iob_bel = iob->bel;
+            Loc iob_loc = ctx->getBelLocation(iob_bel);
+
+            if (!gwu.get_i3c_capable(iob_loc.x, iob_loc.y)) {
+                log_error("Can't place %s. Not I3C capable X%dY%d.\n", ctx->nameOf(&ci), iob_loc.x, iob_loc.y);
+            }
+            ci.disconnectPort(id_IO);
+            iob->disconnectPort(id_I);
+            ci.movePortTo(id_I, iob, id_I);
+            ci.movePortTo(id_O, iob, id_O);
+            iob->disconnectPort(id_OEN);
+            ci.movePortTo(id_MODESEL, iob, id_OEN);
+
+            iob->setParam(id_I3C_IOBUF, 1);
+            cells_to_remove.push_back(ci.name);
+        }
+
+        for (auto cell : cells_to_remove) {
+            ctx->cells.erase(cell);
+        }
+    }
+
     // ===================================
     // MIPI IO
     // ===================================
@@ -330,6 +371,9 @@ struct GowinPacker
                     log_error("MIPI %s is not connected to the output pin or the pin is not constrained.\n",
                               ctx->nameOf(&ci));
                 }
+                if (out_iob->params.count(id_I3C_IOBUF)) {
+                    log_error("Can't place MIPI %s. Conflict with I3C %s.\n", ctx->nameOf(&ci), ctx->nameOf(out_iob));
+                }
                 BelId iob_bel = out_iob->bel;
                 Loc iob_loc = ctx->getBelLocation(iob_bel);
                 iob_loc.z = BelZ::MIPIOBUF_Z;
@@ -383,6 +427,9 @@ struct GowinPacker
                               ctx->nameOf(&ci));
                 }
                 // check A IO placing
+                if (in_iob->params.count(id_I3C_IOBUF)) {
+                    log_error("Can't place MIPI %s. Conflict with I3C %s.\n", ctx->nameOf(&ci), ctx->nameOf(in_iob));
+                }
                 BelId iob_bel = in_iob->bel;
                 Loc iob_loc = ctx->getBelLocation(iob_bel);
                 if (iob_loc.z != BelZ::IOBA_Z) {
@@ -402,6 +449,9 @@ struct GowinPacker
                               ctx->nameOf(&ci));
                 }
                 // check B IO placing
+                if (inb_iob->params.count(id_I3C_IOBUF)) {
+                    log_error("Can't place MIPI %s. Conflict with I3C %s.\n", ctx->nameOf(&ci), ctx->nameOf(inb_iob));
+                }
                 BelId iobb_bel = inb_iob->bel;
                 Loc iobb_loc = ctx->getBelLocation(iobb_bel);
                 if (iobb_loc.z != BelZ::IOBB_Z || iobb_loc.x != iob_loc.x || iobb_loc.y != iob_loc.y) {
@@ -4108,6 +4158,9 @@ struct GowinPacker
         pack_iobs();
         ctx->check();
 
+        pack_i3c();
+        ctx->check();
+
         pack_mipi();
         ctx->check();